First off, to answer your question on spawn points, start up hammer with CSS in the source SDK menu.
All info_player_counterrorist spawns will be the zombie spawnpoints.
All info_player _terrorist spawns will be the human spawnpoints.
(Be sure that you place the spawns correctly because being stuck in a block is really annoying.)
The green smoke in zombie spawn is GENERATED AUTOMATICALLY WHEN A BUNCH OF ZOMBIE SPAWNPOINTS ARE GROUPED TOGETHER!!!
Details in your map are the last thing to really focus on.
Start out with Snap to Grid ON and create almost a main area that most players would gather around in.
Don't expect yourself to make a good map in an hour.
Take your time.
Gather opinions from some of your friends.
Don't forget beta testing (if your map even goes that far).
Here's a link that WILL help you with mapmaking:
http://developer.valvesoftware.com/wiki/Your_First_MapEnjoy