In: Advanced Math
An Introduction of the Theory of Groups - Fourth Edition (Joseph J. Rotman)
If H ≤ G, then show that G acts transitively on the set of all left cosets of H (Theorem 3.14) and G acts transitively on the set of all conjugates of H (Theorem 3.17).
Theorem 3.14 - f H ≤ G and [G: H] = n, then there is a homomorphism ρ: G -> Sn with ker ρ ≤ H.
Theorem 3.17 - Let H ≤ G and let X be the family of all the conjugates of H in G. There is a homomorphism ψ: G -> Sx with ker ψ ≤ NG(H).