You can give orders only when the time is stopped. To do so, click on the soldier, or press left softkey. You can walk by clicking on the ground, or attack by clicking on the alien. To change soldiers press *. To make the soldiers move, unfreeze the time, by pressing the left softkey.
When you have a soldier selected, press # button to change the command. If your soldier has grenade or medikit equipped, you will find its icon here. Psi power of your Psionics can also be accessed by pressing # button.
Keep your soldiers together. Lone soldiers are more vulnerable. A group of soldiers can kill even heavily armored aliens in a very short time. Press 0-button to open a map.
Your psionic has an ability to possess and control any alien, except for the most primitive ones. Select a psionic and choose the "psi" icon and click on the hostile. Since that moment, you control all of its actions, until it is dead or you leave it.
Find and kill all the hostiles.