It's a self-serve frozen yogurt shop.
That's really all there is to say.
You get a choice of what kind of yogurt you like, you can top it with whatever toppings you like, and they charge you by the ounce.
It's pretty good, and only costs a few bucks for a decent (semi-healthy) snack.
If you like frozen yogurt, you'll like Mojo.
If don't, you'll hate it.