Planning is key!
It is easiest if installation begins at one end and cuts are planned out in advance. For a straight forward horizontal wall installation the steps would be as follows.
Congrats! You've made it to the end of the row. Carefully mark your cut and use a box cutter (3 firm cuts on each side, then snap), circular or power saw to make a clean cut. Here's a quick video on how to cut panels using just a utility knife