Platformer - how to make the player die when it falls off the level and they respawn at a checkpoint?

Yes. I know that much. The problem is I don’t know how, what, and where.
These past 4 days I’ve basically been just copy, pasting, and dragging stuff that already came with the platformer’s basic game. I haven’t delved into all the coding and complicated stuff and I have no idea how to get to specific points for the coding and variables and 123 stuff. Hence why I’m asking for help. :,(

Oh, here, like this straight from the tutorial.

"Now that we have the “checkpoint” objects in our scene, let’s add the events. We start with a condition to check to see if there is a collision between the “player” and the “checkpoint”. If the collision occurs, we store the X and Y position of the “checkpoint” object sprite into a scene variable called checkpointX and checkpointY. "

That’s all fine and dandy, but where do I click, what do I click to get to that '[Var] Modify the value of a scene variable.'??
It’s like I’m expected to know all the ins and outs of GDevelop 5 on my computer and how to get to specific stuff when I barely know anything more than copy, paste, and change out the sprites.

I just… don’t understand. :,(