There is a ^ arrow at the bottom left and clicking it will show a menu (clicking the arrow again will hide the menu) of units you must buy units with the Cash (by clicking or holding to by more then one) and move your mouse up or down to pick where they should 'spawn' then you click and off they go slowly to attack or defend from the enemy, units like mono give you money by mining copper of the floor of the map the enemy can do this too to summon a boss if you make it that far that is.
Mindustry Devs / Anuke (Music and most of the Art and Sounds) -------------------------------| New update: -boss -spawning units where you want -unit spawning groups (auto when buying more then one unit) -nerfing crawler -buffing pulser -more expensive pulser -texture change -flame change -health bar change -boss warning -buffed air units -crawlers can't attack air -enemy wave nerf -player buff -core health buff (for both sides) -mono mining laser texture update -mono nerf -nova bullet heal effect bug fixed -healing type unit bullet shrink