When the slingshot is pulled back, the elastic is stretched which adds tension to the bands. Then when flung forwards it sends the object flying.
Hey, I think I can see my house from here!
Okay, this isn't too bad.
Magnets have two different "faces" a north and a south. When north and north are put next to each other, they push against each other which prevent them from connecting. But, when a north and a south come together, they are attracted to each other and the stronger the magnet the strong the connection.