Spawns are simply locations where players appear when the round first starts or after they die. There are two entities involved:
It's usually best to place a team's spawn points in a single location, or at the very least sizable groups. Make sure that the spawn points are facing a useful direction (you will see a graphical representation in Hammer to help with this), so that the players will be able to orient themselves quickly, and never place them in view of a location which an enemy player can access.
Lastly, always ensure that there are multiple exits from a spawn, but no entrances. Doing both of these will help combat spawn camping: it is nearly impossible for an abusive player to cover five or more exits at once, if they can't get past them.