In Buddhism, people can attain enlightenment in many ways. They can also do different things once they are enlightened. One choice is to enter nirvana, where all suffering ends. A person who choose this is called an arhat.
A second choice is to stay in the world to help others find enlightenment. A person who chooses this is called a bodhisattva.
The difference between them is explained in a story.
Two men were wandering in the desert when they came to a compound, surrounded by a high wall. The first man climbed the wall. Giving a cry of delight, he leaped down on the other side.
The second man also climbed the wall. At the top, he saw that the walls surrounded a beautiful oasis with springs and gardens. He wanted to enter the garden. But he thought about all the other people who were wandering in the desert. Instead of entering the oasis he returned to the desert, determined to help other wanderers find the oasis.
One of these men was an arhat, and one was a bodhisattva. Which was which?