Well how to put a gif in a poster will be easy if you have a gif already set and your poster is done open you file and make sure you saved you gif in a gif. format so when you open it it will be a gif so here i made my poster already. You can put the gif in the poster 2 way by erasing some part where you want your gif to be and put the poster infront of the gif so it doesnt look bad or you can cut it out which i am going to do that. So i have my poster and i want my gif to turn out like a traingle so i am going to make a new layer and cut out a traingle shape  Now i am going to try to get the gif to match the way i want it Now i that i did that i cut the gif make sure you do all the gifs I will put the poster behind the gif     Results: The gif isnt suppose to do that but i messed up 

      if i didnt explain it enough and still need help PM me because i felt i didnt do good

sorry for the typos