Mouse handles everything, left and right pan the camera.
A game about warfare in the 28th century, Colony is a strategy game about building and resource management while beating back the enemies on the opposite end of the map, but there are many key differences in Colony that set it apart from this kind of strategy game.
The biggest one in Colony is that you share your base with an AI general. There are eight slots surrounding the central core of the base, four of them are yours, and four belong to your ally. Provided you have the resources (which accumulate slowly on their own or with the aid of certain buildings), you can build on any of these slots. Only the base is shared, not resources or troops.
Colony has are multiple structures you can build, all of which take up one of your four slots, and they can also be upgraded to unlock new units. Structures that are not producing units should either be upgraded or used to generate manpower or money.
You have multiple government types to choose from when you start a quick game in Colony, each one having its own quirks. For example: The Capitalists get resources 20% faster, meaning they can produce more units at higher qualities, which gives a significant advantage in the long run if the game takes a while to clear, and fascist governments build units and structures much faster, which is suited for those who are skilled at managing what limited resources they have in order to get an early headstart or to adapt to situations as they come.
Different units are better against certain types, this is common in strategy games but Colony turns this up multiple notches. Marines while effective against aircraft and snipers are able to take down anything from a distance, Tanks can slaughter dozens of your units in a single shot, and need to be eliminated likewise.
The tutorial explains the mechanics of Colony well enough if you need a more practical explanation on how it works.