I found it hard to generate a structure while listening to the teacher at the same time

You don't generate the structure and make annotations and summary during the lecture or reading, you do those afterwards during your review of your notes.

One key in studying is to not to try to do too much at the same time. Read, then go back and underline or take notes, don't try to underline during the first read-through. Review and condense/summarize then, not while taking the notes. During later reviews, just read the keyword and try to explain it from memory. Active, not passive - the more focused you are on what you are doing, the better you will retain it.