Spawning
There are several spawns used to get to the battlefield. Note that spawning itself does not cost a ticket.
Spawning anywhere other than the Main Base will not resupply your ammo. Use nearby available ammo sources, such as ammo boxes or vehicles, to resupply your ammunition.
Try not to switch kit before spawning in when spawning somewhere other than Main Base, this will spawn you with very little ammo and force you to resupply more, costing more ammo from your team. This can sometimes be a necessity if a FOB you are spawning at doesn't have enough ammo to switch to a role off in person, but does have enough ammo to resupply something essential (such as a rocket for an anti-tank launcher) if you are to switch kit before spawning. If you aren't sure what to spawn in as, what to switch to, or what to play as, inform your Squad Leader of this and ask them.
Main Base
The Main Objective has a spawn on it accessible to the team at all times. It can always be spawned on by anyone in the entire team, is invulnerable to the enemy team's attack, and Servers can often impose additional rules to keep the main objective protected.
Spawn Bunkers
Spawn Bunkers (HABs) are structures built on Forward Operating Bases (FOBs) which the entire team can spawn on. Players can spawn on these structures as long as 45 seconds have passed since the time that they were downed or fully killed (not bled out). Spawn Bunkers can be overran (proxied) by the enemy team by storming a radius around it with their own team's infantry. It takes anywhere from the minimum of 2 players within 20 meters, to 8 players within 80 meters to overrun a Spawn Bunker. Spawn Bunkers can also be disabled if the Radio that enables it to be built is damaged.
Rally Points
Rally Points are carried and placed by Squad Leaders, and can only be spawned on by players in their Squad. Unlike other means of spawning, the Rally Point has a 60 second timer synchronized for every player in the Squad and operates as a "Spawn Wave". If you were incapacitated within 20 sceonds of the Rally Point's timer, that remaining time left is added on to the Rally Point's timer for you, and you must wait the 60 seconds plus that additional time to spawn. For example, if you are incapcitated while the Rally has 5 seconds left, you will miss that wave, and must wait 65 seconds (60 plus 5 seconds) to spawn on that Rally's next spawn wave.
Buddy Rallies:
On the Insurgent Faction, a Squad Leader can deploy a Rally Point remotely on any Rally Point placed by another Squad by right clicking on the Rally Point on the map and clicking Deploy Buddy Rally. Be warned that this will reset the timer on the rally for the other Squad, though.
Mobile Spawn Vehicle
The Western Private Military Contractors (WPMC) Faction has a vehicle available to them on some layers called the Mobile Spawn Vehicle (MSV), this operates essentially as a FOB's Spawn Bunker when it is stationary and has it's engine turned off, but costs 20 tickets when destroyed, makking it the most ticket-valuable asset in the whole game.
Where should you spawn?
For the most part, Spawn closest to your Squad or the Squad leader. If you aren't sure where to spawn, ask your Squad Leader. Note that it is often better to wait for a Spawn to be placed such as via a HAB, Rally, Buddy Rally or MSV, than it is to spawn somewhere irrelevant or at the main base.
"Hold Spawns"
You may hear your Squad Leader ask you to Hold Spawns, this means to not Spawn, and usually is done to wait for a better spawn to become available. If you aren't sure what the plan is, ask your Squad Leader.