When I don’t understand a part in a book I go back and read it. The 2nd time I read it I read it slower than the first time I read it. Or I read every word I did not understand out loud to myself.
Then I get in a quit room then. Then I read it to myself. Then if I still don’t get it I take a little break then I go back to read it. If I still don’t understand it I get a different book.