The sheet is where you go to add new data. Everyone has access to viewing and commenting, but not editing (this is a form of moderation, to avoid potential abuse).
As of right now, I (kala Asi) am the only "moderator" on the sheet, but I am considering getting other folks involved if a need arises.
Changes to the sheet get mirrored to the database.
Open the sheet. Click on the cell that you want to fill out or edit. Leave a comment on the cell. A moderator will later review your change and add it.
Please also comment your contribution on the Credits page.
Same principles apply. Go to the first empty row, fill out the name, definition, and any other information you have about the word you have.
The more cells you can fill out, the better.
No, anonymous users can comment as well.
If you comment anonymously, it is especially important to add yourself to the Credits page.
Primarily translations of definitions to other languages, and commentary on word usage.