The current plans involve bringing along a rocket that could be launched from Mars into a low orbit, where it would meet another craft that would return to Earth.
The vehicle that returns to Earth would carry some kind of Earth-entry vehicle, like a capsule or shuttle plane.
To make the return cheaper by bringing less material from Earth, the Martian atmosphere would be used to produce much or most of the fuel to get the rocket from Mars into Mars orbit.
There are two alternative plans for providing fuel. In the first version, the travelers would carry along some fuel — methane, propane, or hydrazine — to burn with oxygen from the carbon dioxide that makes up most of the Martian atmosphere.
In the other scheme, both the carbon and the oxygen from the carbon dioxide would be used. The carbon would be combined with hydrogen carried from Earth to make methane to be burned with the oxygen.
An unmanned spacecraft might be sent to Mars to make the fuel even before humans leave Earth.