Same way you learn anything, read all about it then use what you read to implement something. When the something you implemented works and solves the problem, you've learned something! Repeat forever with different things (and sometimes with things you haven't done for a while). Each time you learn something new.
Exams are a hacky stand-in for actually using a concept to solve real world problems.
Exams are a hacky stand-in for actually using a concept to solve real world problems.