electromagnetic force
Great question! When you lean against a wall, you don't fall through it because of a force called "electromagnetic force." The atoms and molecules in your body and the atoms and molecules in the wall repel each other due to this force. It's kind of like when you try to push two magnets with the same poles together. They push each other away. This repulsion prevents you from passing through the wall, keeping you safely on the outside. So, thanks to the electromagnetic force, you can lean against walls without falling through them.