It's not an app for posting photos exactly (even though it is), it's an app for showing people things. Here's my food, here's my outfit, here's what I was doing today, here's what the sunset looked like on my vacation. It's an interesting take on communications between people. It has its dark side (people going out of their way to "get the gram" so they can be envied by their friends instead of just trying to enjoy things organically; people, especially young women, who become overly pressured by their peer group to look and act a certain way) but when used well it can be a nice way to keep up with what your friends are doing. Think about it like a modern take on post cards.