build/move units using the mouse. the control panel at the top of the screen has all the build orders, which you can now lock in place.
i forgot to tell you guys the enemies dont stop coming. you will get overrun eventually, its just a game of how long before you get killed. there's now a difficulty select option wherein lower difficulty setting boosts your units' life. added alien kill cash bonus. the units are now cheaper and stun times are reduced.
TIPS, you can actually telefrag units you dont like (yours or the enemy's). use the passive behavior if you want to save a unit for killing a specific target like mortars. use the support panel a lot. mine at the center of the map first, retreating as the game progresses so that you dont run out of mine sites very soon.