how do you take over a planet once you got a coleny ship?

You need to deploy your colony ship to an empty planet slot by using the Fleet link.

it dident work it said action impossible

Click on the Fleet menu.

Type in the number "1" (replacing the "0") in the far right field next to the colony ship.

Click "Continue".

Type in the coordinates of the empty planet slot where it says "Target".

Make sure you have enough deuterium to make it to the Target location.

Press "Continue".

Click on the button next to "colonize".

Click "Continue".

It is now deployed to colonize.

how do you know if no ones in it

It will be an empty space, NO planet will occupy it.
Think of it as you making the planet

Use the Galaxy link (from the Empire Menu on the left) to look for empty planet slots.

ok thanks i got a planet! how you change name now?

In the Overview screen (from the Planet Menu) click on the word "Colony" (to the right of the word "Planet"). It will open the Rename/Abandon Colony tab.

i sent a ship to colonise to a grid i wanted to colonise(x1)
twice to diffrent locations.

i got an espionage message that they could not find the planet and came back "demoralsied:-)"
i re-checked and the slot was still empty.

any explanation guys?