The construction is a generalisation of the left regular representation of G. The latter is the special case where H = {e}, the trivial subgroup of G.
If gH is a left coset of H, then the stabilizer of gH
is the conjugate of H by g, i.e.
the stabilizer equals gHg-1 = {ghg-1
| h
H}.
Indeed, for each element ghg-1, with h
H, we have
ghg-1gH = ghH = gH.
And, on the other hand, if k
G
satisfies kgH = gH, then there is a h
H with kg = gh, from which we deduce
k = ghg-1.