sirlois, many many servers are MODDED. that means they downloaded things that let them do special stuff. i remember being like you when i was new, except i was worse cause i wasn't on PTT2.
as LGM said, looking around the sections near the bottom of the page will help.
for codes like you asked for, you'd want to get ACAS (Art Crazy's Admin Script.) There's a topic somewhere...
you can't go in the servers cause the blue bar reaches the end and then does nothing, right? well that's cause the map inside is a MOD. it's a map that doesn't come with TT, but that someone created with TGE or Modwiz. most are very fun, but in order to play on them you need to download Map Packs. i downloaded a few, and i STILL can't get anywhere
. However, i haven't downloaded Dazzle pack, which has TONS of MODs, Gametypes, and upgrades to TT (Think Tanks). (oh, and not to worry you, but when i got Dazzle Pack my video card happened to break right when i opened TT, forcing me to get a new comp... but the old comp was old, and it works for most ppl, so don't worry.)
To make a server with your own maps, find a post on how to use modwiz (you'll need modwiz, of course.)
Those Gametypes are specially downloaded. you can download and host Gladiator (i think), but rollerball can only be hosted by a few people. however if you download rollerball, you can enter rollerball servers and play. also for the race GT, that you just need modwiz. people make race maps, and use ACAS to make the GT called Race.
Making UFOs fly is in ACAS.
All in All, you can normally wait out some mods. so if the server won't load, wait a few minutes, then it might.
Hope i could help, and have fun Playin'!
All this info may not be completely accurate, so someone correct me if i'm wrong, because i'm kinda new too.