If you have sprained something, like your ankle, it means you have hurt it by twisting it too much.
When you sprain something, it can make you feel a little bit sad or uncomfortable, but it's usually not too serious.
Examples:
She sprained her wrist playing soccer.
I sprained my ankle when I fell down.
He sprained his knee while running.
I hope I don't sprain my arm picking up this heavy box!
She's so clumsy, she could sprain something just walking down the street.
I've never sprained anything, but I'm always careful not to.