The basic idea is to stage components of a large manned mission in a high Earth orbit, where you have already imparted the majority of the energy needed to get to destinations in the solar system. The $\Delta V$ to get from LEO to a high-Earth orbit with an apoapsis at the distance of the Moon is 80% to 85% of the $\Delta V$ to get from LEO to Mars.
You can use highly efficient electric propulsion systems to get to HEO, since you don't care how long it takes for uncrewed components to get there, in order to minimize the launch mass, and thus the cost. These can be fueled chemical propulsion stages, habitats, and other pieces. Our Moon then provides a convenient and nearly free means to both raise and drop components' periapsis for storage in a circular HEO, rendezvous with a crew, and to use a low periapsis for a near-Earth chemical propulsive maneuver for efficient injection to an interplanetary trajectory.
See this article for an overview of the concept.
A stable way to store such pieces is in a DRO around the Moon, which is energetically cheap to get into and out of from HEO. You can also put some of your returned hardware, such as your deep-space habitat, in DRO for resupply and reuse.