Following on from the previous post after restarting nemo you get right click options to encrypt or sign files.
Slight tangent here to do things like this manually from the command line you can follow the instructions here.
So far from the gui method I have managed to figure out how to encrypt documents / files etc. Then decrypt then.
I am not sure fully what I am doing here, so may have to do more research, but hopefully these two posts will help you get started.
There is also a useful guide here.