Beautiful is used when you describe something or someone.
This girl is beautiful.
The landscape is beautiful.
Lovely can also be used to describe something or someone (more similar to かわいい). Something that is cute, pretty.
BUT "lovely" can also be used to describe someone's behavior.
Your friend buy you a coffee.
In this situation you can say to your friend: "thank you! You are so lovely!".
"Lovely" because your friend did something nice for you. :))
I hope it helps :)) がんばってね‼︎（＾ω＾）