question about learning to talk?

My son is 13 months and at the point where some days he babbles a lot with the pointing eeh.. stage.. He has said a lot of words not but not in context and only a couple of times, other then mama dada (he has been learning animal sounds to though) . But he does do this thing where one week he would be big on talking then others walking.. now he is walking so im thinking he is going to go back to talking...

So this is my first and im kinda learning the how they learn to talk.. but it seems like so far it went from that just random babble with no actual sounds to forming sounds and froming the different sounds. Well now he hasnt talked in a few days and when he started talking again it seems like he is saying new letter sounds and not the old ones to. SO  is this how they start to learn to form it to words, by just learning lots of sound and then forming? i know its changing but cant understand exactly how other then noticing different sounds but still cant understand it. lol

I am not rushing him or worrying i just love to watch him learn and grow and i just notice that its changing again and it just makes me so excited to see him learning

just wondering if any of those other mamas notice this change or am i crazy haha!