You need to upgrade your factories in a certain order. Scouts are available at first, after that you can get a ripper factory, you can construct transport facilities after that, and finally you can build barges. This is the basic fleet, and these ships are available to every race. The one ship you absolutely need is the transport. Without transports, your troops are trapped on your planet, and can be killed by any player who has enough troops to do so. A second very important ship is the barge. Without barges you can't attack. Well actually it is possible to attack, but you won't gain anything, only suffer losses. The two other ships are best used to minimize your losses, as an escort, or to scare away attackers. To learn more about ship types, study the orbital combat or ship classes areas of this manual.