They r great as bonfire material
But seriously, it depends on the subject and person:
Humanities: They will have lots of definitions and examples, I know for religion the textbook is written by the chief examiner so when they give a definition, u know that the definition is the example of a full mark answer on the exam. And those questions do come up and can be some easy points. Go through the paragraphs, search for the key sentences which gives an exact definition, example, explanation etc. Highlighting and then making notes from that (hand written is best but honestly I think typing is fine) is a great way to internalize and gain thorough understanding. The questions in them r meh, some of them r good if done in exam condition but some of them r just boring filler so don't do all of them.
English textbook: lol
Science: Notes should be made, but differently from Humanities. First, read the chapter, take a look at the concepts, make sure u really understand what's going on. So it is more read and think about the science behind the text. This is now where the questions come in, u don't have to do them all, but for some of the easier ones, take a glance at them see if u can come up with answer in your mind and then double check this with the solutions. Only bother writing out answers for some of the more tough ones that u personally struggle to come up with on the spot. For working out problems, do a couple from each "style" of question so u know how to do them. Correct the questions as you go and make sure your being honest about where you went wrong, how they get answers, check your expression etc. After this, make notes. Notes are not super helpful for all sciences but can be excellent to have. Write down definitions u don't know, make summaries of the theory in ur own words, maybe grab some diagrams and examples of working out that u still struggle with. Come exam time, u will be grateful to know what areas need improving and it also serves as a great refresher. I do science notes online, up to the individual.
Math: This is the most unique one. First thing first, read the quick intro theory and look at examples. Then dive straight into questions, do many, practice significant portions of questions until u r sure u got a solid understanding. Practice the hard ones, *GLANCE* at the solutions for help if needed, correcting as you go. For notes, don't do online, get a separate work book. Have a page at the front which indicates what topics that r in the note book. At the start of each new topic, have a big title. Talk about the general theory behind the math, write down formulas, how to use them what they mean etc. After this write out examples of problems and the method behind solving them. Use the questions u got wrong to guide this section. Include the question or label what type of question it is. In a test this can come in very helpful. These notes will generally be derived from the text book questions and what the teacher has told you. Try to write out how to use CAS on various sections as well. Maybe print out some solutions to areas u r 100% lost in and hope come test/exam time the solutions r similar to exam questions if u r allowed notes lol.