I was playing around and adding props such as trees and crashed gunships to my map in zero editor but when I saved and tried to play in-game nothing is there and it is just a flat map. Anyone know what this is? Any help would be greatly praised

Sounds like the old common issue...

Your msh/odf folders must exist in data_mod\worlds\mod

If you open zeroeditor and open objects from within the assets, that doesn't work.

When you want to add shipped objects you must copy them from assets, into your world's 3 letter world folder

Some times it's also safe copy effect and munged folders, you need those for animated props like doors so they work properly.

Edit: this tutorial helped me do all the basics like adding objects, vehicles, water, and other things.
http://www.gametoast.com/viewtopic.php?f=64&t=19725

Welcome to GT!
Did you actually munge your map? If yout haven't you should run the VisualMunge.exe located in data_XXX/build. (XXX is your map's 3-letter name) Be sure to run it with administrator rights. If it munges very fast and no changes are applied to your map, then download the Munge Fix. Also before you start doing anything and asking question look through the Everything you need thread. And pay attention to what Anthony said too.

Yes I have munged twice and was just learning the basics. So I decided to add some trees and a crashed gunship and nothing appears in my map.
Also I didn't know I had to put world assets in my "ABC" folder I thought it was in the "Worlds" folder. Thanks guys. Also I did and I couldn't find anything like that.

is the BF2_ModTools in a C:/ folder?

Yes, it is.

Does your VisualMunge seem to work properly? Have you done what I said about it in my post before? If you have and the error still persists try doing a manual clean+re-munging, reinstalling the game and/or the modtools. If it doesn't work, well... I don't know how else I could help you.

Yes, actually I installed the munging fix. I'll just see what works. Thanks for the help all.
EDIT: I wasn't munging after I made edits. I didn't realize. Although my trees are floating and have weird black leaves. IDK why.

Regarding those black leaves, you need to enable hard-edged transparency for the leaves' material(s). http://www.gametoast.com/viewtopic.php?p=466539#p466539

Okay, thanks. Would someone mind answering me one more question, how come after I put my custom unit skins in my sides folder and munge they do not appear in game? My heavy trooper and clone engineer have my custom skins(Screens: http://i.imgur.com/AP8XieE.jpg and http://i.imgur.com/GW0Nolp.jpg) but my normal clone trooper does not? Same thing with my stormtrooper. Any help would be appreciated.

Make sure that your skin is named properly-->rep_inf_ep3trooper.tga (I guess you edited the original one, so that should be good)

It definitely has the same name. I opened it in the msh Viewer and the skin looked good (In my opinion. http://i.imgur.com/UUV5OLz.jpg this is it if you wanted to see), so I munged the IMP side and I have the default white skin.

I can't possibly guess what the problem is. Try a manual clean then remunge.

Okay, thanks.