Missiles are stored in a separate inventory, shown by the missile icon in the top right corner of the screen when you’re wearing a helmet from the mod. To increase your max missiles simply stand near a missile expansion block (this will make more sense in a few updates)
Missiles are automatically moved to this inventory from your normal one if there’s room in it, firing missiles only draws from this inventory and will ignore missiles in your normal inventory. To use the charge combos, simply charge the beam you want fully then press F, these sometimes need a large amount of missiles to fire one powerful projectile (20 is the most one will cost), or sometimes will fire a stream of projectiles and use missiles the longer you hold down the button. Missiles are homing, the wavebuster is homing, the sunburst shoots a field of light energy that damages anything near/in it, the darkburst opens a hole to the void and sucks mobs in, the flamethrower is a flamethrower, the ice spreader shoots a projectile that freezes and hurts everything around it and is way underpowered right now (it’ll completely freeze them and do alot more damage in the next update), the wavebuster shoots a beam of energy that seeks out anything alive with the intention of kicking its ass and will proceed to do so, it will also bounce between enemies, the sonic boom fires a blast of energy that does immense damage to anything within a 4 blocks of the point of impact and travels (almost) instantly to the target.