Export the lot from the game, creating a Sims3pack file.
Click Submit in the top of the front page. Choose Sims 3.
READ THE LOT SUBMISSION GUIDELINES. Most lot rejections can be avoided simply be reading the guidelines.
Click Upload from my computer. Click Proceed.
Choose the file (browse to the Sims3pack on your computer). Click Upload File.
Wait for file to upload (may take several minutes depending on file size).
Fill in the information such as title, description, etc. Read carefully because missing information on this page, or doing it incorrectly, can result in a rejection.
Click Update Item.
Click the Uploads tab to Preview the creation. Edit if needed. If you don't need to edit, place a check into the box and click Submit Selected.
Wait for lot to be approved or rejected.