How do you merge fleets?

Ive been trying to look up how to merge fleets, and its says the ussual same hoohaa of "custom name" "leader skill" and "fleet size" but idk what to make out of that, and also the part where it says there must be atleast two military fleets of the same size. I find it all raelly confusing, and idk if its matters but i do play on console