Ok.
I'm makeing developer maps.
ex. devmap game/mp/level1

now, I don't want users to go through all that.

So, how does a map(s) become a mod?

You need to create a definition file. This is a text file that contains the information about your level. Then your level will show up as available for play in the game. I assume this is what you want rather than making the player load a completely separate mod for the game for playing just one map. This text file would then be saved in the same location as your map as levelname.def where levelname is the name of your map.

You should look at the files that came with the game (or read my quake 4 book linked in my sig). it should read something similar to:

mapDef game/mapname {
"name" "Some Name"
"DM" "1"
"team DM" "1"
"Tourney" "1"
"CTF" "0"
"arena CTF" "0"
}

it could be more or less complex.