Let G be a Lie group. We make G×G operate on G on the left by (g1,g2)x=g1xg2−1. Let ρ be the orbital mapping of e. Then the restrictions of T(e,e)(ρ) to T(e,e)(G×{e})=Te(G)×{0} and to
T(e,e)({e}×G)={0}×Te(G)
are isomorphisms of these spaces onto Te(G). Hence T(e,e)(ρ) is surjective and KerT(e,e)(ρ) admits for example the topological supplement Te(G)×{0} in T(e,e)(G×G). Thus ρ is a submersion at (e,e). Hence G is a left Lie homogeneous space of G×G.
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.