Step 2: Cut the angle in the back legs.
All of the cuts are perfectly straightforward except for the diagonal of the back legs. I've attached a picture of how to do this, which I think is easier to understand, but just in case you are a word person, here are written instructions, too.
1. Lay the leg down so the 20-cm wide side is parallel to the ground.
2. Measure 42 cm up from the base of the leg.
3. Measure 12 cm from the opposite edge of the leg across the top edge. Make a mark.
4. Using a ruler, draw a line from the top mark to the mark at 42 cm from the leg base.
5. Measure 42 cm from the base on the other side edge, draw a line across. You won't use this line for the cut, but you need it later.
6. Using the circular saw, cut along the diagonal line.
Do that twice.