let's say your filename of the video was ANCHOR3.ZNM (which is one of them), you would copy that video into the folder that contains the grisc program and then you would open a command prompt.
You should get a nice black screen where you can type:
grisc ANCHOR3.ZNM
and that is all there is to it.
I'm a mac guy, but I spend a lot of time at the command line in OSX too
