Go to main menu and press "Space". (Or whatever other button you have binded as "default action")

You need to destroy the ArmA Logos for each DLC.

Destroying targets may drop healing for you.

If targets make it to the end or you shoot purple targets, it heals the enemy. (Some white targets also heal enemy: ambulances, unarmed choppers)

Destroy all DLCs for the achievement. (and some golden boss thing)