Copying files, installing things. Anything that requires to be "written" to the SSD itself. Read would be as it says on the tin, reading a file aka opening things up.
You shouldn't use an SSD to install loads of programs because it can shorten it's life, an SSD works a lot differently to a hard drive as in it uses flash memory. It has to move and wipe the area which can cause a build up of garbage as its called. So using an SSD like you would for a hard drive is not recommended. Your SSD may load games up quick but that's about it, once you're in the game nothing will change compared to a hard drive