... or maybe it's barren, radioactive, toxic, or other extreme world. You have to research techs before you can colonize them.
warfrick is playing DL, so there's no extreme colonization tech in the game.
My guess is you're right about the right-click thing.
p.s. warfrick, if you're on a full keyboard and turn off Num Lock, you can use the number pad to move ships one square at a time. 1, 3, 7, and 9 are the diagonals and 2, 4, 6, and 8 duplicate the up, down, left, and right arrow keys.