Look at it this way: A stick man in a two dimensional world. If you poke him with a pencil, all he can see is the slice of the pencil. What does the third dimension do? It allows us to see the pencil. AND to go from the stick man's feet to his head outside of his two dimensional world. He doesn't realise the pencil is there. What does our fourth-dimensional time do? It allows us to go from one point on time, from the early times, to later times. So a fifth dimension might allow us to travel through time?

Supersymmentry is a mathematical concept. The universe doesn't make mathematical sense as we know it. Add a fifth dimension, and wow, it begins to make MORE sense. Go up to 11 dimensions and it makes perfect mathematical sense. It is one of many hypothetical theories with a little science behind it.