A master of laws

hi, i study in international relations/3rd year/, so i am planning a master of law from US. What should i do?

You need to supply more information; as written, your question is too vague.

Why law school in the US?
(Do you mean JD?)

a master of Laws, i.e., LLM, is primarily for international students that already have a non-US law degree*. If you do not currently have a law degree, then you can apply for a JD program in the US.

*An example,
https://hls.harvard.edu/dept/graduate-program/llm-admissions/