TLDR: In a BOM view click the "Add To Shopping List" button. Select the Shopping List you want to add the BOM to and the multiple of the BOMs parts you want to add to the Shopping List. Click the "Add" button and the parts at the appropriate multiple will be added to the Shopping List.
All the details:
Navigate to the BOMs app in the navigation and click into it. Click into one of your BOMs. For me, I'll select "PHIL'S BOM".
In the upper right corner you'll see the "Add To Shopping List" button, like this:
Once you click on the "Add To Shopping List Button" you'll see a modal pop up asking you to pick a shopping list and enter the quantity of the part you'd like to add to the Shopping List. The Shopping List selected will also show you the shipping address and number of lines in the Shopping List.
I'll choose "Fall Production" and add a quantity of 20 of PHIL'S BOM to the Shopping List which looks like this:
Click "Add" to add them to the Shopping List.
If you navigate to the Purchasing app and then Shopping Lists, you'll see the Shopping List now has a larger number of items. For me, a total of 12 item which reflects the number of parts needed to manufacture the relevant BOM at the multiple requested.
In this example the 1 part I added previously was also included as a part necessary in PHIL'S BOM, which had a total number of 12 lines, so I see 12 lines total since the multiple of 50 of the JS102011SAQN that I added before was aggregated into the multiple of 20 of PHIL'S BOM. Now in the Shopping List I see a total of 70 of theJS102011SAQN which is the 50 individual parts plus the 20 I need for my BOM.
This concludes the explanation of how to add to a Shopping List from the Parts or BOMs app.