How do you land large colonization facilities, landers, etc. in an atmosphere that is 1% as dense as Earth's? With supersonic retro propulsion on a rocket that

How do you land large colonization facilities, landers, etc. in an atmosphere that is 1% as dense as Earth's? With supersonic retro propulsion on a rocket that can be reused. How do you then have enough fuel to leave? You don’t, so you need to make the fuel with robots landed on one-way missions first. Luckily there are plenty of raw materials on Mars (in the atmosphere, soil and water deposits). It’s very hard but it’s certainly doable if you can do the first part.