Every gametype will either use an info_player_deathmatch spawn (DM Spawn) or gametype_player spawn (Gametype Spawn).
The info_player_deathmatch entity is used by DM and TDM. It has no team affiliation, and requires no keys aside from the "origin" key which is automatically determined when you place the entity. You can set an "angle" key to determine where the player will face when he starts. Gametypes whose .gametype files specify "normal" spawning will use these. Players will respawn at a (semi)randomly-chosen info_player_deathmatch point as soon as they are killed. (I say semi-randomly because the game takes into account how close a spawn point is to living players when it choses the spawn.) I will refer to this as a "DM Spawn" point. These should be placed fairly regularly about your map, and you should have as many as you think will be necessary to accomodate as many players as will populate your map at peak capacity. Too few, and you are likely to have telefragging, where a player spawns "on top" of another player.
The gametype_player entity is used by gametypes that require separate spawn points for the Red and Blue Teams. It requires that you set a "spawnflags" key to specify which team the start is for. "spawnflags" "1" designates a Red Team player start. "spawnflags" "2" designates a Blue Team player start. gametype_player also requires a "gametype" key. This key designates what gametypes the spawn will be used for. For instance, "gametype" "elim ctf inf" would be used for those three gametypes. In the stock Raven maps, each team typically has 16 starts for each gametype, for a total of 32 players. (It should also be noted that you can have a situation like mp_shop (The Shop Under Siege). In The Shop Under Siege, the 16 "spawnflags" "1" gametype_player entities have "gametype" "inf elim", which means the Red Team starts in the same place in Infiltration and Elimination. However, there are 32 "spawnflags" "2" gametype_player entities. 16 are "gametype" "inf", and 16 are "gametype" "elim". This means that the Blue Team starts in one place for Infiltration, and another place for Elimination.) Gametypes whose .gametype files specify "interval" or "none" spawning will use these start points. I will refer to this as a "Gametype Spawn" point. For most gametypes using these spawns, you'll want to place the Red Team together in one location, and the Blue Team together in a separate location. Specific spawn information will be given in the gametype entity\trigger profiles on the Gametypes List.