Interstellar traveling with speed of light doesn’t get far. Distance between places in the universe is unimaginably so far.
So scientist have to figure out a way to go faster than light. But the problem is as you learn at school you can’t travel faster than speed of light. However if you understand the space time carefully, you can’t travel space through faster than light, but space can do what ever the speed it can get breaking the light speed barrier.
The idea of Warp drive invented assuming the concept of moving the space faster than light.