What Math to Learn for Machine Learning?

Question

Neural networks

Hello, friends. I'm going to the army soon (in a month). I want to get into machine learning. And I don't want to waste time.
Question one: I want to hear the opinion of a professional, is it worth studying at all? I think that this is the future, and an interesting thing.
Question two: What books on mathematics would you recommend for machine learning to read in the army, my knowledge of mathematics is average or slightly below average.
THANKS IN ADVANCE.