First, take a really long tube that extends into space, bend it around a space station, have it come back to earth and form a circle with the start of the tube. Next, shoot a gun up the tube really fast. The bullet’s momentum will lift the tube and you can also bleed some of the energy from the bullet and store. Once the bullet hits the bend at the top it will also “lift” the spaces station which keeps it in orbit. Then just do the opposite for the bullet on the way down.
Maybe an oversimplification but pretty much that’s the gist.