How do you make a respawn and checkpoint script?

I'm making a game with many levels, but they are all in the same scene. It's like Super Mario Bros, you start off at the beginning, and if you die, it respawns you back at the beginning. But when you pass the checkpoint flag, the game saves and next time you die, you go back the that checkpoint. You see, I want to do that for my 3-D game. I want to make it so that when you fall, you hit an invisible object that indicates that you died and then respawn to my last checkpoint. So my question is, how do you make checkpoint scripts and how do you make respawn scripts (and anything else I might need)? I'm very new to Unity, and I am brainless when it comes to scripting, please explain as simple as possible and provide a script for me to copy and use. Thanks a bunch! :)