Hey Pamela,
So you are creating a new assembly item. Filling in the required field and then saving the screen. After you save it you should be able to click on the Bill of Materials tab. Once on this tab if you click new, the grid should open up. Add 2 items to the list and then hit update. The grid should save and display the 2 items you have added.
Are these the steps you are taking when adding line items to the BOM?
Can you tell me your account name also, I will check to see that the new screens made it to your account.