Well, it's a bit complicated, and the full details would take a really long time to explain, buuuut~!

[Improv time. Bridges finds himself a nice oval shaped rock and holds it upright, making his other hand sit behind it and wiggling his fingers like makeshift rockets.]

Your most basic spaceship was just a small shuttle. They could only hold a small crew of like, maybe four to eight people tops? Anyways, they basically built ships that would sit like this, and they kind of like... used advanced fireworks to make go racing into the sky? And eventually they'd break out of Earth and be floating around space! It's pretty amazing stuff, still.