Once you have commited your warlords in the command phase how ever there on diffrent plaent and there are 0 enemy units on that plaent what happens.

There would be a battle there that you would most likely automatically win at the start unless your opponent was to get a unit there with mobile or ambush or some other type of trickery.

so you would win the the plaent lets say its not the 1st plaent your warlord retrats to HQ and then the HQ phase

Yes which lets you trigger the Battle action if you want.

You win the Battle, but do NOT add the planet to your score area.

Just wanted to clarify that, as 'win the planet' is a little misleading.

And another point to remember is you don't win the battle until the battle has initiated at that planet, for instance if it's Planet 5 and I sent my Warlord to 3, we would resolve 1, 3, and then 5, allowing for action windows and such.