You can assume that blocks added directly to the workspace are executed all the time. Strictly speaking, such blocks are executed every frame.

Exceptions

Blocks of function definition

Blocks within a function are executed at the moment the function is called.

Functions can be used repeatedly.

Event blocks

Blocks within an event are executed at the moment the event occurs. This moment is determined by the internal logic of the object, hidden from the user.

Events can be used repeatedly.

Example

Block 1 will be executed once at the moment of loading the scene - it will turn on a light bulb in white.

Block 2 will be executed every frame - when the blue button is pressed, the light bulb will turn blue. That is, the block will constantly check to see if the blue button has been pressed.

Block 3 will execute the function defined in block 4 - when the red button is pressed, the light will turn red. The event is defined in the code of the button, it can be seen as a shell over block 2, giving the user a more convenient way to interact.