If something is done solely by someone, it means that only that person did it, and no one else helped.
The word solely can make people think of independence and doing things alone.
Examples:
She solely made the cake.
I solely cleaned my room today.
The toy was solely played with by the little girl.
He solely ate all the cookies in the jar!
The superhero solely saved the city from the bad guys.
The cat solely caught the mouse in the house.