Your brakes are hardworking pieces of your kit that you need to check on regularly. You may not think it but bits and pieces of gravel can get stuck in your pads, causing scratches on your rims.
For v-brakes, what you need to do is to grip the calipers and unhook the noodle, as you would when you take your tire off. With an allen wrench, remove the brake pads.
What I hate is that very few mechanics know how to properly toe in a brake pad. The theory is that the front edge of the pad should be the edge that touches the rim first. If you don’t do it right, you get that annoying squeal when braking. You also have to line up the pads so that they sit completely on the rim and not slightly off the edge. If it’s too far off towards the spokes, you’ll develop a lip on your brake pad from the wear and may cause the brakes to stick. If it’s too far off towards the tire, there is the possibility of flatting as well as creating a lip.
Saul, the mechanic in the first video, is using a Tacx Brake Shoe Toeing Tool to do the job.
In the second video, Todd gives a very thorough explanation on how to replace disc brake pads. Try to avoid contact since the oils from your hands and fingers can contaminate the pads and the rotors.
For your disc brake pads, remove the wheel and put in the spacer. It is important because sometimes, people erroneously squeeze the brake levers when the wheel is removed. What they don’t know is that since the disc brakes nowadays have self-adjusting systems, they will grip past the point where a rotor can fit and it will be very hard to separate the pads.