7. Mark angles for miter cuts

You cut your first angle.  Now put the board on the floor and measure how long you want the board and make a pencil mark.  From your pencil mark, draw the new angle direction on the edge of the board ... you want your angle to be the opposite of the one you just made ... this can get confusing.  So, like the photo above, mark the angle on the board to remind yourself.

Turn the angle on the miter saw, and cut to size.  Generally you want to cut on the line - or a little on the outer edge of the line (see below).  Remember:  ALWAYS ERR ON THE SIDE OF TOO BIG than too small!!!