Step one is to lift people, fuel, and equipment to either LEO or Moon orbit, and assemble a trans-Martian space vehicle in space.
Step two is to send the trans-Martian space vehicle to Martian orbit, and ultimately to a soft landing on Mars.
The SpaceX plan is to refuel the second stage in LEO for the trip to Mars. On Mars the fuel will be manufactured for the return trip.
A Moon base greatly increases costs and the time to attempt a Mars mission, which is why the government likes that plan.