Your instructor will teach you how to assemble your gear, and then you’ll practice breathing on scuba. You’ll practice a variety of different scuba skills in the pool, including:

Proper breathing
Finding neutral buoyancy
Using hand signals to communicate
Different types of finning (kicking)
Using the inflators and deflators on your BCD
Equalizing
Removing your mask, putting it back on, and clearing the water from it
Removing your regulator (mouthpiece) and using a backup
You must also demonstrate that you’re a capable-enough swimmer to do scuba diving. You must pass a swim assessment that requires you to:

Tread water for 10 minutes (you can’t touch the sides of the pool)
Swim 200 yards (there’s no time limit and you may use any swim style)
In some courses, this segment is completed on a single day, over 6 to 8 hours. The open water dives make up the final segment of your Open Water course.
You’ll complete then 4 open water dives in which you’ll perform most of the skills that you practiced in the pool. You might also learn a couple new skills, like learning how to enter the ocean through surf, or how to leap off a boat in scuba gear.