Safety Check
Both climbers should be wearing a helmet to protect from rock or equipment fall and other hazards. Both should have a harness that is snug and with the buckles properly fastened (double back).
The climber should tie in with a figure 8 follow through knot.
The belayer should thread the rope through their belay device and locking carabiner, with the carabiner attached to their harness belay loop and locked. Make sure the climber and brake strand are on the correct side of the device (typically there is a diagram on the device).
A stopper knot should be tied in the end of the rope to close the system, so that the rope cannot accidentally pass through the belay device during climbing or lowering.
The rope should be flaked out so it runs smoothly. The climber should have their climbing shoes on. Make a plan with your belayer. Explain what you plan to do when you reach the top of the climb (typically you will lower). Now you're ready to climb!
Keep track with this checklist!
Belaying
Commands
Climbers should communicate with a pre-agreed upon set of commands. Here are some common ones:
"On belay" - Climber is checking they are on belay. When ready, belayer should respond "Belay on".
"Climbing" - Climber is checking whether the belayer is ready for them to climb. When ready, belayer should respond "Climb on".
"Take" or "Tension" - Climber asks belayer to pull in slack. Belayer can respond "I've got you" or "Tension on".
"Slack" - Climber asks belayer to let out slack. Belayer can respond "Slack on".
"Watch me" - Climber asks belayer to pay close attention to a particularly difficult part of the climb and be particularly prepared to catch the climber in case of fall.
"Rock!" - Hazard alert! Something has been dropped (rock or other piece of equipment).
"Ready to lower" - Climber notifies belayer they have reached the top of the climb and are ready for the belayer to lower them down to the ground.
Process
The strand below the belay device is called the brake strand. The belayer should never take their hand off the brake strand. In order to pull rope through the device without taking their hand off the brake strand, use the Pull-Brake-Under-Slide method (PBUS).
Here's a quick video showing the process:
If at any time, the climber is not moving, rest both hands on the brake strand to better catch a fall just in case.
Watch the climber and pull slack through the belay device as necessary. Communicate when necessary with commands. Once the climber reaches the top, they will call "Take". Pull them tight and wait for the climber to say "Ready to lower". Then move both hands to the brake strand, and slowly lower the climber by letting the rope slide through both of your hands. The climber will lean back and walk down the wall.