1) play games (probable on managed rooms only; managed mean room has a bot like springie etc)
2)xp = points, see 1)
2a) in a managed game, you do not have all technologies like factories or units or superweapons. if you unlock them, you can build them. in a gameyou host on your own, you can, however, disable unlocks, so you have everything from the start. ... on the other hand, there are moduls and weapons, which you can equip for your different commanders. once unlocked, you can design up to 5 commanders using the wabsite of zero-k. on game start, you can select on of these 5 models.
3) what do you mean? if 3a) read there
3a) if you mean in battle, how to recycle a unit/building, just use a unit with building capacities, like constructor or commander and press "e" or use the pink recycle icon. then leftclick on the structure or unit to recycle. gives refund of up to 50% of the total metal back.
edit: corrected 50% instead of 40
