Using Forge 2.0, you have to do a thing called "tagging." Ever opened "advanced" and seen "tag" without anything there? That's what this is for!
Here's a simple way to tag something:
1. Open up the gametype you're making on the map you're making. If you want an object for CTF, open up CTF. For Assault, open Assault.
2. Create the object you want. You can technically make a bomb spawn on a flag stand, but generally, it's flag stand for flags, the plate for bombs, and the object spawn (the big blue arrow) for anything else.
3. Use the B options of the object, and go into "advanced." Change the "tag" to the object you want there. For a flag, I believe it's "flag_spawn." You do need a "flag_drop" or something like that for where you put the flag too.
You can also do some very odd stuff with tagging. I found a KotH map where a Warthog is the hill, and you rack up points as long as you're on the Hog.
I suggest checking ForgeHub.com for tutorials and help. I think we have a list of what the tags to. I suggest checking that.