The basic goal of each player in Coldest is to destroy the opposing team's base. It is possible for there to be more than one base per team, but only one needs to be destroyed in order to win the game. Each player selects a mech, weapons, and an item based on the amount of salvage that they have. Both teams initially spawn from their base, but may place additional spawn points at strategic locations as the game progresses.
This section is particularly subject to change because I'm not quite happy with the current system.
After a player is killed, they must wait 15 seconds before they respawn, and they are given a small amount of salvage to allow them to purchase a new mech. In order to afford more expensive mechs they will need to destroy opposing team mechs, allowing them to collect additional salvage from the wreckage.
It is also possible to return to a spawn point and change loadouts. However, doing so will require the player to wait for the full respawn time as if they had been killed. It is currently the only way to replenish ammunition for weapons which are low or out.
There are two ways for a player to restore HP after they have been damaged. The first is simply to wait. Over time the mech's internal repair systems will slowly repair armor and damaged components to restore HP. The other is to power down using the P key. This will restore full hitpoints, but during the time that the mech is powered down it is unable to move or fire and thus is very vulnerable to enemy players. Note that this does not restore expended ammunition - only returning to a spawn point as noted above will do that.
Standing in water allows the mech to improve its cooling efficiency, but deep water can also slow its movement.