To add more detail, 법(法, as Aurelio said) means the law or rule. For example 상법 means commercial laws, 헌법 the constitution, 법룰 the law (in formal context), and a whole slew of them.
It is also used in words like 방법 (方法) which means a way or method of doing things, since that implies a rule too.
In your example, 법 is short for 방법. It is a compresesed expressoin. Spelled out, it'd be 한국어 공부 방법(methods of studying Korean) or even 한국어를 공부하는 방법 (Methods by which you can study Korean).
So your example shows a couple of characteristics in the language.
One is the tendency to contract and compress phrases (한국어를 공부하는 방법 -> 한국어 공부 방법 -> 한국어 공부법).
Secondly, in Korean you can sometimes stack nouns together to create a phrase involving an adjective and verb. For example, "화재시 대피 방법" (How to Escape in Case of Fire). In English, it's hard to express it with nouns only, but 화재(fire)시(time) 대피(escape) 방법(way) or its short form 화재시 대피법 is essentially a string of nouns. This kind of noun stacks can pose some difficulty for learners.