if you have your controls set to default you go to edit mode by pressing up on the D-pad and then you press X to spawn something :b . Hope this worked.
you can go to forge and make it that you can
if you are saying how do you make your own world in halo reach, use forge mode to make a map.
You cannot make your own maps in Halo: ODST, it doesn't contain forge world. Halo 3, Halo: Reach and Halo 4 all contain forge world.
i do belive there will be a forge to make maps like Halo 3 did.
For "safe havens" infection.
EASY: just go into forge-RjFx2
die at least three times
Go to Forge mode and make that C-130.
Go to forge and make a map and then you go to the menu and slecte add map in halo Reach
Halo 3 Forge is a feature that allows you to build maps. You can't make the map designs from scratch, but you can place objects to make the map's psychology. Although here are a few glitches to make it more unique! By setting an object u can set to not set on start and then by starting a new round you have a few minutes to seconds to place an object inside it to make it custom. Also Vehicles do not set correctly when doing this.
Just make a normal forge map then seclet juggernaut
No forge maps are designed to be made by and for the community you can't charge for that