Adding or modifying an entry on AniList is an easy task. The main focus is making sure that data is accurate and as complete as possible for that moment in time. All sections of the form are formatted in a similar fashion and have handy tool-tips to assist you.
New Characters and Staff can only be created through the anime and manga forms' Character and Staff sub-pages. This is the same whether you are submitting a new entry or editing an existing one.
Existing anime and manga entries can be edited using the edit button at the bottom left of their page.
Existing staff and character entries can be edited using the edit icon button at the top right of their page.
When a user provides a submission it will undergo a review process where a moderator can approve or deny the additions and/or changes made - it is extremely helpful to provide as many sources as possible to confirm the information you want to submit.
Please be aware that AniList does not handle all entries the same way that other sites do.
Episode 0s and Prologues are only placed in a standalone entry if they aired in a different format from the same series.