When something skyrockets, it goes up very fast, like a rocket going to the sky.
When something skyrockets, it usually means it's going up a lot and very quickly, which can be good or bad depending on the situation.
Examples:
The price of the house skyrockets.
Her grades skyrockets after she starts studying more.
The number of people at the party skyrockets when the famous singer arrives.
The demand for the new toy skyrockets after the commercial airs.
The temperature skyrockets to over 100 degrees in the desert.
The cat's popularity skyrockets after it saves the baby from a snake.