Okay so imagine you have a box of crayons, and you use different colors to draw a picture. But if you close your eyes and rub your hand over the picture, you can still feel things like bumps and roughness or maybe smoothness.
Textures in art are kind of like these feelings you can get when you touch something. It's how the picture looks like it might feel if you could touch it.
So if you're drawing a picture of a puppy with shaggy fur, you might use lots of lines close together to create a rough, hairy texture. If you're drawing a shiny apple, you might use smooth curves and shiny colors to make it look like it's almost glistening in the light.
Textures in art make the picture more interesting to look at because it feels like you can almost touch it with your hands.