Transport Modules

Please help me. I'm all set to invade mars, but I don't know how to.

If Mars is uninhabited, you need to have a colony ship, and you move your ship on to the space that Mars (or any other >0 class, non-toxic world) occupies.

If Mars has been taken over by some other race, then you must either:

1) Invade, by creating troop transports (or the more advanced Combat Transports).   This requires you to have researched certain technologies in the tech tree.   BE AWARE that invading another race's planets will tend to have consequences.

2) If Earth is a planet you control, it's probably got some pretty good influence values, and Mars is likely to be in your sphere of influence.   Build the influence on Earth and surrounding planets until the people of Mars rebel and come over to your side.

You might be able to trade for it, too... who knows.

As above, if the planet is uncolonized a colony ship will do. You seem to already know that, but I've learned never to take things for granted.

If it belongs to someone else, you need to research Planetary Invasion. This is in the same tree as ship weapons and defenses, so you will need to research a few techs into that before ti branches. If you're playing Twilight, your tech tree may have different names for similar techs.

Once you have the planetary invasion tech, you need to build a transport. The premade Transport ship will work, but most people design their own ship to minimize costs - transports are like colony ships, they are one-use only. The preferred direction to transport design is to put only the transport module on the cheapest hull you can fit it on. Add engines only if necessary. Range is almost never necessary. Weapons are also optional and are rarely needed or wanted.

Don't you invade with the transport ships? So shouldn't you have weapons?

Transport vessels need not be armed--just clear out any enemy ships from orbit with your own regular combat ships before sending the transports in.