How to make my 2D character roll

Hi. Welcome to Unity (and Unity Answers).

1st Possibility:

I've created a game and I saw in the sprites folder that my prefab character could roll

...do you mean you downloaded the character and there are sprites for a rolling animation in that folder?

but I dont know what do I need to press because its not "ctrl" or runand "ctrl"

...if my above sentence is true, then that doesn't mean the caracter prefab is set up to do those animations, you might have to implement this functionality. Check the readme or the scripts included with the prefab.

2nd Possibility:

You are a complete beginner and you just started using Unity. You think that an animated sprite is enough for the character to move controlled by buttons. In this case you should look at the beginner tutorials provided by Unity. You can find them in the Learn Section.