Green flag and take the "define" blocks. How it works: When you enter a number in the fps variable in the block, it divides itself by (itself*itself). It uses the result of that equation for the delay. For example, if you entered 4 fps, it will divide itself by (4*4), which is equal to 16. 4/16 is 0.25. This number will be used for the delay of the action.
Custom block I made that demonstrates working with Frames Per Second, also known as FPS. Credit to Scratch Team for sprites and sounds.