Just make sure you get high grades, take challenging classes, graduate with a decent class rank, and get a good score on the LSAT. Law schools look at your undergrad GPA and LSAT score among other things when deciding whether or not to admit you. But your grades and LSAT score are the most important factors across the board.
You have to go to law school in order to actually study law; there’s no undergraduate alternative or equivalent like in other countries, especially in European ones. In the US you have to get a Juris Doctor from a law school. You can get a master’s in law and even a doctorate, but these are not worth the hassle unless you want to practice tax law or teach.
In law school, you’ll have set first year classes such as torts, property, constitutional law, contracts, criminal law, civil procedure, and a legal writing and reasoning class. After your first year, you can pretty much take any classes you want, although you’ll need to take professional responsibility and you’re advised to take classes such as evidence, criminal procedure, corporations, family law, and trusts/wills/estates.