I'm sure there are books that could help (Paula Begoun of Paula's Choice has written a few but I've no idea if they're any good) but there are also a lot of online resources that are probably more useful tbh. For me, a great starting point was Caroline Hirons' cheat sheets https://www.carolinehirons.com/page-category/cheat-sheets and especially the one about confused skin which explains in what order to treat skin ailments. If you work your way through them I think they will provide you with a really good basic knowledge of skincare. Also, as someone who has had problem skin since my teens, the best 'learning resource' for me has actually been a really good medical beautician - if you have a good one near you and can afford to go even for just one facial it might be worth considering. Sorry, not a book-related answer at all!

I'm a 21 yo who is just beginning to work on my skin and I don't know where to start. I'm looking for books which can help me understand my skin better and work on it.
Please suggest.

Books on skin care