How do I load troop onto a transport?

When you get the message that it's been built and the game takes you to the planet view, select the ship from among the icons representing orbiting ships. Those icons are in a box on the lower right. Once it's selected, you need to adjust the slider bar below that box, where it asks you how many troops you want on it -- it defaults to half the selected planet's population. Then push the green "Launch" button.

When you launch them, the screen under where they're shown in orbit changes to a slider. Select the amount and hit launch. Unless, you've set all your planets to auto-launch. In which case it'll launch as soon as it's built as if the slider was in the middle (2500 mil, if combat transports). With transports you can reuse them, so you can send them back in to orbit (it'll distribute the troops on it evenly throughout the planets) and relaunch them if you have to.

~SDC~

To select double click the ship,then follow as stated above.

Thanks, guys. Works great!

"In which case it'll launch as soon as it's built as if the slider was in the middle (2500 mil, if combat transports)."

While colony ships auto launch as if the slider was in the middle, combat transports and normal transports autolaunch with a full load.