The CTF contains 4 new techs (permanent powerups) and a new weapon (not so much of a weapon really) the grapple.
You need to have a copy of CTF.
You will also need 20mb of free hard drive space on the same drive as quake2.

If you have both of these.
Make a copy of the pak's from the ctf folder to the 3zb2 folder.
You should not overwrite any existing pak .. select no and rename conficting pak. You can use names pak0 to pak9
3zb2 CTF also supports Lfire CTF Maps.

CTF Maps :

q2ctf1 "McKinley Revival"
q2ctf2 "Stronghold Opposition"
q2ctf3 "The Smelter"
q2ctf4 "Outlands"
q2ctf5 "Capture Showdown"
q2ctf6 "Borders Canyon"
q2ctf7 "Zorigomi"
q2ctf8 "Boxed In"
q2ctf9 "The Hangar Scenario"

Don't forget you need the chn's for these maps