There are 2 separate buttons that you can use to create a new BOQ. One is located in the top left hand side of the page, and the other is on the left hand side of the Layers area (next to the Save button).
Once you select the Add New BOQ button you will be greeted with the below popup. This is where you can select from the list of Entity/User Tools to create your BOQ from. Once you've selected your Tool you can select which Sub-Location 1/Page you want to assign this BOQ to. Now that you've filled out each field hit the ADD NEW BOQ button at the bottom and your BOQ will be created and you're ready to start marking up.
Pro Tip
You can select the "Show Auto-Filled Fields" to make any adjustments to the Tool/Settings before creating the BOQ. This will ONLY apply to this specific BOQ that you're creating and will not change the base Tool.