We're going to be very blunt here: the IMDb is not a cocktail party, so it's not enough to just say you are a producer or writer to get listed; you have to actually have a finished project that has been seen by people other than your mother and your best friend. Or, to put it another way, we don't list names, we list credits.
Further, you have to have at least one on-screen credit to get listed; just sitting in the bleachers for a crowd shot at a football game isn't good enough.
OK, let's assume you should be in the database but aren't yet. As the previous discussion implies, the first step is to make sure the title you appeared in or worked on is in the database. If it isn't, you'll need to add it.. You can add your credit as part of the process of adding the title, but please be sure to include some of the other people, like the director and the lead actors.
If the title is already in the database, just click on the "Update" button at the bottom of the title's page and choose whatever category applies to the work you did. If you worked on a TV series, then you should try to add yourself to the specific episode(s) you worked on, not the series itself. If there are missing episodes, use the "Add Episode" button on the series page to add them.