[Begginer] Character & Weapon modeling and animation doubts

Hey, I’m entering in the world of modeling and animation but I already have some doubts =P
I make a character and the animation, and create a weapon and animation, how do I put the gun on the character to be in the right place and at hand? I need to make an animation for each weapon? I’ve seen some models of weapons with arms, what’s the point?

Thanks!