The current Mars rover mission also has an experiment to test the feasibility of creating fuel from the atmosphere. The whole Starship to Mars plan hinges on the ability to create fuel on site, so the results of this experiment are going to be extremely important. Once they get that squared away/figured out, and figure out an ideal landing site for the first manned mission, then they can start launching Starships to Mars for the purpose of creating fuel and transporting supplies/cargo in prep for the arrival of humans. Probably send approximately 2 years worth of food, backup water supply and oxygen, habitat modules, modules to grow food, surface transport vehicles, power generation, etc. The initial waves will also need to autonomously begin to manufacture fuel for the return trip and store water/produce oxygen.