Review how much energy and water a building needs in pop-up menu when you move cursor on building icon. After placing a new building you need to connect it with energy or water if building need any; make sure to connect power lines and water tubes to the right places on the South-West side of a building. If a building don't have water/energy, the warning icon will appear.
Hire new colonists via "HIRE" button on the bottom-center of the screen. Colonists need food and oxygen.
Review colonist's needs in the bottom-right corner by clicking on him. You can change the name or fire the colonist.
Set job for each colonist at "JOBS" window. It's not necessarily, but can make your colony and colonists more effective.