This question has options. How would someone go about accomplishing this goal?
How can you make a circular saw guide?

Select from: (I) Attach the two pieces with glue and tape at exact right angles to each other. Make the right-hand arm of the guide a bit longer than the distance from the blade to the left edge of the saw's shoe; the first time you use the guide, the saw will trim off the excess. From then on, just line up the right end of the guide with your cut mark, and cut with the shoe against the shoe guide for a straight, square cut.; (II) Attach the two pieces with glue and screws at exact right angles to each other. Make the right-hand arm of the guide a bit longer than the distance from the blade to the left edge of the saw's shoe; the first time you use the guide, the saw will trim off the excess. From then on, just line up the right end of the guide with your cut mark, and cut with the shoe against the shoe guide for a straight, square cut.;
(II)