Cutting planks to length at the end of a row, you just need to score the laminate layer well and then bend the plank backwards. It will snap along the score. I used a rotary cutter that looked like a pizza cutter and it worked well. Give it a few hard passes to score it deeply.
On rows, there is very little waste. What you trim off one row you can use to start the next row (as long as the piece is at least 12" long). That staggers the seams.
Each row interlocks with the previous row. When you reach the last row at the end of a room, or a bump-out, where a full width plank is too wide for the remaining space, you trim the plank to the required width on the "leading" edge that does not interlock with the previous row (you trim off what doesn't fit in the remaining space). You leave a small gap to the wall for expansion that gets covered by molding.
Note that it is intended to leave an expansion gap around the outer edge. The trimmed edges won't be perfectly clean, like the factory edge on the plank, and row to row won't be a perfectly even edge. The system is designed for DIYers. The edges all get hidden by coordinated quarter-round molding. If you end at a doorway, there are coordinated transition strips. So it all looks clean and finished when you're done.
Trim the width the same way--score the laminate side well and then bend the plank backwards along the score. If you have a countertop or piece of lumber, line up the score along the edge of the countertop or board, and fold the waste edge down. Try to fold it evenly until the whole length of the score is creased, then you can give it a sharper fold. The waste edge will snap off.
If you have to "notch out" a corner, like a section of wall adjacent to a doorway, where a portion of the plank will be full width and a portion will be partial width, use a utility knife to cut all the way through the plank for the short cut. The long score will then be free to bend to snap it off.
It is basically waste, some fraction of one row per room.