Those will either be in the Community menu or Database. You can find the collection link under Community, and then at the top you should see a Browse button. From there you can then add items from scratch.
The easier method is to browse to a colorway in the database by drilling down into the model, and then by color. From there, there should be a button to add the item to your collection. This will again bring you to the collection 'add' page, but the information will be mostly filled in.