I'm not sure what you mean by "mask these shapes over my video." If you use the Shape layer as an Alpha Track Matte then you will only see video in the triangles. If you use Alpha Inverted then there will be holes in the video. These are basics that you should know.
You'll need to toggle the Modes/Switches layer or press the middle icon at the bottom left of the Timeline to reveal both the Switches and Modes columns to find the track matte options.
Im not to sure how to use the shape layer as an Alpha Track Matte? The only other way I am familiar with trying to get what i want is by copying and pasting my video footage, once i have mask a triangle over it. However I then cannot rotate the middle triangle without the footage rotating. I then cannot make sure that all the footage in ieach triangle is perfectly aligned so it looks like it is one piece of footage and not three individual layers.
AE Basics. If you don't know how to make a track matte then type track matte in the search help field and follow the links.
In your original comp put the triangles on top of the video
In the Switches/Modes column find the track matte column and click on the pull down to select Alpha Track Matte
If you do not see the Track Matte options press f4 or click on the Toggle Switches/Modes button at the bottom of the timeline.