After you open Zeroeditor you first need to load your ABC.wld(ABC is an example of a modID) file, then the next thing is to change layers to the conquest layer or whatever gametype you are working with, then press the "F" key so you can actually see your map, lol, then do whatcha gotta do.
Another thing that i find to be helpful is to click on SHOW/REGIONS at the top of the toolbar so you can locate your 4 default CP's easier.
Unless you are an experienced mapper, i wouldn't try to do anything too extreme to start out with, start simple and practice with a few things until you get the hang of it.
Play around with the ZeroEditor tools and get a feel for how they all work.
Try adding 1 command post first, then maybe add 1 vehicle spawn, mess around with the terrain a little and raise it or lower it and make some hills or holes lol.
You should probably make your first map a "Test Map" and just use that map to experiment with different things, and when you figure stuff out you can then put that on your real project map and you know it's done correctly and you won't have to worry so much about spending 2 weeks working on a map just to have it all fall to pieces near the end and have to start over from scratch.
Don't forget to save your progress frequently in Zeroeditor, if you do something wrong it may crash and you might lose the work you spent so much precious time on.