There are a lot of books that explain UI/UX design. Learning from books only helps in some instances. Through that, you will gain only theoretical knowledge. But one can remember the subject for a long time through practical experience. For that, I suggest you take training where you get a chance to learn from experts. If you are planning to learn it from online training then I recommend you to take up this UI UX Course offering by a highly recognized institute like Intellipaat.
Before that do check out this free UI/UX complete course video -