Chemiosmosis is one of the main unifying things between most types of life - it is present in all types of cell - prokaryotic, eukaryotic, and all subdivisions of these. It is, in its most essential form, a way of generating ATP. ATP is the major energy currency in living cells, as it is the thing which powers all cellular activities. For example, the sodium potassium pump which is used to maintain a concentration gradient of sodium and potassium by pumping sodium out of cells and potassium in relies on ATP. Another name for ATP is adenosine triphosphate, and it is formed when a phosphate group is attached onto a molecule of ADP - adenosine diphosphate - and it is this phosphate group which is removed to provide the energy. Due to the unstable nature of this bond ATP is very short lived, and so is not a useful energy storage for long periods of time unlike starch and glucose which are very stable and can last for a long time - like a potato.
This ATP is therefore very useful, and it is generated much like a hydroelectric dam. In a hydroelectric dam, water moves over a turbine and this turns a generator and electricity is produced, while in chemiosmosis protons (H+ ions) move across a semi permeable membrane and turn ATP synthase. ATP synthase is an enzyme on the membrane which is spun by the incoming protons and this spinning leads to the binding of an inorganic phosphate group (PO4) to ADP to produce ATP.
It is believed that this mechanism may suggest an origin of life. In alkaline water vents proton gradients exist naturally and it is not a big jump to assume that it is possible that proto cells made of iron may have formed naturally on these vents which may have been the precursors to modern cells - as these protocells adapted to the surroundings they may have evolved a basic ATP synthase which and pumping mechanisms which allowed them to generate their energy portably, thereby giving the first cell its ability to live separately, and therefore allowing the development of life as we know it.