I just bought the Master-Level membership to DnDBeyond and I'm really enjoying figuring out how everything works and generally how to use it. 

Can someone tell me if it is possible to import physical books I've bought in the real world into the App/Site?

I have quite many books and I really don't want to have to spend even more money just so I have access to them online via the App/Site. 

If you know whether or not this is possible, and how to enable it, I'll be extremely grateful! 

Thank you so much! I hope you and your family are all staying safe and healthy!

          〜 Ev 

It is not possible, and the reasons why are explained very well in this thread

You can use the homebrew feature to recreate spells, subclasses, feats and races from the books.

also you should be made aware you can just buy the pieces you need for the characters and items you need added to the srd stuff.