So I'm currently orbiting a planet and I want to go to hyper speed. But when I press GO I get this

Error 4048E-17: Unable to engage the hyperdrive motivator due to gravity well.

Anyone know what is happening?

You need to exit the "gravity well" (the red area around planets and suns)- to do this, first you'll need to go into sublight and get to an area that doesn't have a gravity well. You most likely won't see the red areas until you opt to travel in sublight first. Once out of the gravity well, you should be able to use Hyperspace normally.