Sedimentary rock looks like the name says. Rock that is built by layers of sediment. So it looks like layered rock. It can look quite different one rock from the other due to the different types of sediment making up the layers. BUT you can tell it's sedimentary rock by it's layers. Hope that helps you.
Depends on where you got it from. Since it is composed of a whole bunch of other things it will look different every time. From the bottom of the ocean, near a shoreline, or near a river, its composition will be different.