So while they’re still dangerous, modern wingsuits are now technologically advanced enough to allow pilots to actually gain altitude after leaving the drop zone and come ever closer to achieving flight. The basic aerodynamic principle behind that is when downward momentum meets resistance in the air or atmosphere, lift ensues. Flight is a whole lot more complicated than that as you add in thrust and drag to the equation.
But this vid, from Squirrel Wingsuits, demonstrates lift perfectly. It looks as though it was shot somewhere in Utah in an ideal locale to capture and use air currents.