Instagram makes my photos blurry , why?

[Jessica Rios]

I have an android. I see sooo many people upload collages, and every single picture looks perfectly fine and clear. When I upload a collage, it is too big and will only get half the picture. And make it blurry? Can someone please tell me how to make the image smaller, so that it will upload completely and what the size of an instagram picture is? What app helps me do this? Please help! thanks