You probably don't need to be a master at it before going to university. It's essentially a programming language for maths, so if you have some familiarity already, it should be adaptable.
Youtube is a good resource though. So is the MATLAB website. It really depends what you want to do - But you can find "projects" online to test out as well.
For first year you will probably use these sorts of MATLAB skills: Variables, matrices, storing outputs (A goes to A1 for use later, etc), plots and maybe differentation/integration type operations. 9 times out of 10, it's just typing in the words and letting the software do the rest.