How do baseball players remember all of those complicated calls that managers make?

Question

Like when they're touching their caps, noses, ears, etc.

Answer 1

Practice.  Many of the signs you see are just gestures and not really signs.  The coaches and managers will go through a series of none signs until the give a sign that is an indicator the the sign is coming.  The players ignore all the rest until they see the indicator and know the sign is coming next.  They also have incentives to learn and remember the signs - if they miss a sign they are fined.

Answer 2

they parctice them before playing