I want to get into a non-bugged version because I hear this a lot! My group couldn't use turrets >.<
In my group last night the healer couldn't figure out how to use the turret, so she healed the rest while we used the turrets. It's extremely easy. There's no fire button. It shoots automatically. You use the mouse to aim the turret and it shoots the bugs. Shoot the big white ranged attacking ones first.
If you put your healer in the middle to heal everyone (this is probably the easiest strategy since it can cover up for a lot of mistakes) make sure you all face inward and shoot over each other's backs so you can make sure the healer never gets bug aggro.