How to Find Spawn Points
As you walk across a map, keep an eye on your minimap. If you see red dots appear, you may have just stepped on a spawn point. This is easiest when there are no other players around.
If you think you just found a spawn point, take a step or two backwards, then go forwards again. If more enemies appear, then you have probably got one. You should be able to pace back and forth here to make enemies to your hearts content. Be careful you don't make more than you can handle

Auto-Spawn
In most places where there is a spawn point, you can trigger a near endless supply of enemies. This is known as Auto Spawn. There are several ways to trigger it, but the simplest way is to pace back and forth at the spawn point, and stop directly on the spawn point. You may need to pace as the flow of enemies slows.
Blocking Spawn Points
Spawn points seem to have a front and a back. This is important to know in player groups. When one player is spawning, everyone should stay behind him. If someone stands too far forward (on the spawn point, or in front of the spawning player), the spawn will cease. This is known as blocking the spawn
At times, you may wish to do this if there is far too many spawn for the group to deal with. However, do it too much and you can anger other players.
Warnings About Spawn Abuse
Intentional blocking of spawns when players are trying to grind, to irritate or annoy others, is not acceptable. This is considered ruining the game experience for others. You may report this to a game moderator if its a problem. Offending players will be warned, and punished if they refuse to co-operate.
Over-spawning and/or swarming, with intent to kill others, may be considered ruining the game experience for others. If done, repeatedly, with little or no provocation, it is considered abuse and may be punishable by a game moderator.
There are times when it may be considered acceptable; usually these instances involve instigation from the other player. It all depends on context, and punishment is at the discretion of the moderator involved. To that end, I advise not doing it at all if you can help it.