Go to this URL:
https://www.squidge.org/dsa/cgi-bin/upload.cgi or click on any of the links for "Posting Interface" or "Upload Story."
The Posting Interface's instructions are very complete and clear and will take you through the process step by step.
Some explanations about terminology are below:
1. Title. Type in the title of your story. Don't type in anything except the title of your story. Make sure you have spelled it correctly and that everything that should be capitalized is capitalized. Typically, articles (the, a, an), conjunctions (and, or, etc.), and prepositions (in, on, of, etc) are not capitalized unless they are the first word in the title.
2. Author name or pseudonym. Type in the name by which you want to be known when your writing is discussed or mentioned. Make sure that you use the same spelling and the same manner of capitalization for your name or pseudonym every time you archive a story. Otherwise readers will not be able to reliably search for you by name.
3. Author's website. If your story or stories can be found at another website, fill in the name of that site here. The first part of a URL, http://, has already been put in for you. Add the rest of your URL after the second slash mark. If your stories can't be found at another website, you can leave this blank.
4. Email address of author. Type in the email address at which you would like readers to send you feedback. Make sure it is spelled correctly. Use an address you expect to keep long-term.
5. Category. Select one or more categories which may apply to your story. Click the up or down arrows on the box to scroll through all possible categories. Windows users: To select multiple categories, hold down the control-key and click on all the categories that apply. Mac users: To select multiple categories, hold down the command-key (apple key) and click on all the categories that apply.
6. Rating. Click on the pull-down menu and select a rating for your story. Rating choices are G, PG, R, and NC-17.
Note: Use your own judgment with regard to the content of your story. Stories rated G are generally considered to be acceptable to audiences of all ages, containing virtually no sexual content or violence. Stories rated NC-17 are generally considered to be intended for adults-only due to extreme sexual content, violence, or both. These ratings apply to both slash and gen stories. Explicit sexual content, regardless of the gender of the participants, should be rated R or NC-17.
7. Warnings. Select none, or one, or more warnings that may apply to your story. Click the up or down arrows on the box to scroll through all the possible warnings. Windows users: To select multiple warnings, hold down the control-key and click on all the warnings that apply. Mac users: To select multiple warnings, hold down the command-key (apple key) and click on all the warnings that apply.
Note: The following definitions apply to the stories found on this archive. They were not carved in stone or handed down to me by a higher power to serve as definitions of these categories for all of fandom. If you email me to tell me these definitions are wrong, I will laugh my ass off and mock you when I talk to my friends.
Gen: A gen story is one that does not contain homoerotic relationships between main canonical characters and other canonical or non-canonical characters. It may or may not contain heterosexual sex. Gen stories with explicit heterosexual sex or explicit violence will be rated R or NC-17.
Slash: A slash story is one that contains homoerotic relationships involving one or more main canonical characters. It may or may not contain explicit homosexual sex. Slash stories with explicit homosexual sex or explicit violence will be rated R or NC-17.
Violence: There are varying degrees of violence. A punch in the nose is obviously less violent than ripping someone's head off. Use your own judgment with regard to what level of violence in a story requires a violence warning.
M/M: This warning is not necessary if you have already included a slash warning. A gen story with homoerotic content involving secondary characters should carry this warning.
M/F: This warning is generally used on slash stories that also include heterosexual sex. I'm not about to start policing this warning, so don't ask.
F/F: This warning is generally included with the slash warning, to indicate that the homoerotic content of the slash story occurs between two female characters.
Death Story: This warning indicates that a major canonical character dies within the story.
Rape/NC: This warning indicates that some variety of forced sexual contact will occur within the story. Violence may or may not be involved.
H/C: Hurt/Comfort. This warning indicates that in the course of the story, one character will be harmed in some way and other characters will offer comfort. Violence may or may not be involved.
B/D: Bondage/Domination. This warning indicates that some variety of consensual bondage and/or dominance/submission content, usually sexual, will be occur within the story. Violence may or may not be involved.
S/M: Sadism/Masochism. This warning indicates that some variety of consensual sadism/masochism, usually sexual, will occur within the story.
Multiple partners: This warning usually applies to stories containing characters involved in sexual or romantic relationships with more than one other character. This may include threesomes (such as F/V/K, etc), or serial relationships (such as F/V, F/K, F/T, etc).
AU: Alternate Universe. This warning applies to stories that take place outside of the canonical "universe" of the show. Examples include stories set in the distant past or future, stories set in fantasy worlds, stories involving odd mental or magical powers, stories involving mythical creatures, etc. An AU may also be a story that intentionally ignores a point of show canon or branches off from canon before the end of the series and takes a different path -- such as, a story that takes for granted that third season never happened, or a story that takes for granted that first and second season never happened, etc. You're going to have to use your own judgment here, too. If you're not sure, write to me and ask. I won't bite.
None: Choose this if none of the warnings above apply to the story.
8. Pairings. Select one or more pairings that may apply to your story. Click the up or down arrows on the box to scroll through all the possible pairings. Windows users: To select multiple pairings, hold down the control-key and click on all the pairings that apply. Mac users: To select multiple pairings, hold down the command-key (apple key) and click on all the pairings that apply.
9. Summary. Type in a brief summary of your story if you feel like it. You don't have to if you don't want to, but it will help people decide if they want to read the story. The summary should not exceed two or three sentences or lines of text.
10. Author Notes. Type in anything you want to say about the story -- you can thank beta readers here (you do have beta readers, right?), thank your friends, thank people who helped you, say something about your inspiration for the story, whatever.
11. Spoilers & story notes. Type in any information about the story that was not included in the summary or author notes. This may be detailed warnings, spoilers, explanations, etc. Whatever suits you.
12. Disclaimers. Type in whatever disclaimer you feel like using. Disclaimers provide you with absolutely no legal protection whatsoever, so please don't assume that a disclaimer will keep you safe if the copyright police come calling. This is completely optional.