Which exercises are aerobic?

Running. Running/cycling/swimming/hiking/ are all great aerobic exercises. Look for anything that gets your heart rate up and keeps it up for a time.
Raise heart rate. Aerobic exercise raises your heart rate. Brisk walking, jogging, running, cycling (regular bicycle or stationary cycle), swimming, water exercise, water walking, treadmills, ellipticals, stair-steppers are examples. Ease into it slowly. If you have a heart condition, ask your primary or heart doctor first.