Base jumping is when people jump off of tall things, like buildings or cliffs, with a parachute to help them float back down to the ground safely.
First, they have to find a good spot to jump from, which is important because they need to make sure they have enough room to safely land.
Then, they put on a special suit that will help them move through the air and keep them warm, because it can be very cold up there.
Once they are ready, they take a deep breath and jump off! The wind rushes past them as they fall and they can see everything around them getting smaller and smaller.
When they get close to the ground, they pull a cord on their parachute and it opens up, making them slow down and land safely on the ground.
It can be scary and dangerous, so only people who are very experienced and have been trained properly should do it. But for those who are brave enough, it can be an incredible experience that they will never forget!