I love books and I love to read as obviously do many other people. Although electronic books may be gaining in popularity, most books are still physical. If you gather books at any rate close to mine, eventually you need to go through them to both organize and get rid of unwanted and unneeded books. Here is the method I use that also works very well for many other people.
First I go through the books with a quick pass to get rid of books I no longer want, need, or can fit into my storage spaces. Some books will simply be out of date and useless, like 5 year old computer manuals for software you no longer have. These are obviously garbage and they go into the recycle bin.
There may be some books that perhaps you just do not like or have read and enjoyed and have no need to reread. A lot of fiction falls into this category for me, as well as children's books my kids have outgrown. These are obviously useful are go into the "donate" pile. I'll also place great books I hope to reread someday in the future into the donate pile simply because I do not have infinite storage space for books nor do most people. For example, I love "War and Peace," and hope to reread it some day, but when I do I can borrow someone else's copy or simply buy it again. I do not need to physically own this book until I maybe get around to rereading it in maybe a few decades.
Where can you donate these books? I'll often let friends have a first pass through to see if they want any of them, and then the swap shop at my local dump may get them or maybe Goodwill. Children's books sometimes get given to schools, especially schools for the under privileged as they are generally under funded and can use them.
Next I generally do some sorting of my books. Long term storage, ones I infrequently if ever need to access, go into the attic or basement. Books I access often, for example technical and other reference books, go into bookcases and on shelves in my office or the den, both of which have a fair bit of book storage. And books that fall in between go into the other bookcases that are scattered around the house.