There are several different ways to cut vinyl planks, depending on your experience level, tools, and the thickness of the plank. Be sure to check the manufacturer instructions for more specific methods!
Score and Snap
The simplest way to cut a vinyl plank is by scoring and snapping. Using your t-square to score a straight line, lightly score the vinyl plank on the surface side using a utility knife. You’ll need to make several passes.  Then bend along the score line to snap the plank in half. Some people use their knee as a leverage point to easily snap the plank.
Tile Cutter
Another way to cut vinyl planks or tiles is by using a tile cutter. This can be purchased or rented from a hardware store for a one-time use.  You’ll want to measure and mark the spot where the cut will be made. At this point, it’s as simple as pulling a lever to make the cut.
Circular Saw
If you have the tool available and are proficient with its use, a circular saw can make a great cutting tool. You’ll want to use a fine-tooth blade and work slowly, as to not melt the vinyl plank.