There's several things you need on top of the TrenchBroom editor. When you make levels with it it will save .map files. These then need to be converted to the quake .bsp file format (which is in turn placed in quake/id/maps).
To create a .bsp file you'll need a BSP program, a Light program and a Vis program.
You can download these tools from here -
http://disenchant.net/files/utils/tyrutils-0.5-win32.zip

Next you'll want to make compiling your .map to .bsp super easy so download Necros compiling program -
http://shoresofnis.wordpress.com/2010/03/30/ne_q1spcompilinggui/

And you'll also need to get yourself the textures used in Quake to create your levels, the one that has all the standard textures in one .wad file are here -

https://www.quaddicted.com/files/wads/id.wad.zip

Also the help document for TrenchBroom is here -

http://kristianduske.com/trenchbroom/docs/ 

You will need these tools:

http://disenchant.net/files/utils/tyrutils-0.5-osx.zip

and the compiling GUI doesn't run on the Mac. You will have to look at the command line parameters of the tools, I'm afraid. Are you familiar with the Terminal? 

So those tools won't help. Are there native Mac versions available somewhere? Has someone ever attempted to port BJP's compilers? 

(stop beating me to it) 

ported BJPs tools to OS X, but I haven't published them. But I will provide OS X builds of rebb's tools at some point. 

My brain was half-asleep! :P 

The main thing I love about open-source communities is that everyone is always so eager to help, even if their brains are half-asleep :D
I have windows installed on my Mac (boot camp), so I guess I can download those utilities for windows and use those. From what I understand, these formats are cross-platform compatible, right?
And I've already downloaded the WAD and read the help :)
Thanks again 

I use Terminal now and then, so I'll also give Mac utils a try :) 

If you can use Windows, I would just use Windows. Tools and utilities for the Mac are few and far between...

But yes, the file formats are all compatible. 

Tyrann's tools are readily available for the Mac, so there's really no need to go to Windows for this. Also, the quakespasm engine (quakespasm.sourceforge.net) is cross-platform and runs very well on the Mac. 

You can get by, yes. But you don't have many choices. There's usually one of everything so I hope you like it! :) 

But tyrann's tools are pretty good! 

That they are. 

and the compiling GUI doesn't run on the Mac.
rats, i've been thinking i should remake that gui in java for cross platform. :( 

So I've made my very first map in Trenchbroom and saved it as .map. Now I have a probably very silly problem - I'm clueless as to how I should install qbsp and other utils. It's not as simple as a double click, is it? Thanks! 

Just place the compiling programs in the same folder as your .map file and run them like this -

qbsp.exe mymap
vis.exe mymap
light.exe mymap

Where mymap is the name of your map... once you have run all three it should load your level! (just hope you put some lights in there and also the info_player_start entity!) 

You'll also have to copy the BSP file to your "quake/id1/maps" folder. 

Open a terminal and run the following

cd <path to your map>
./qbsp mymap
./vis mymap
./light mymap

Notes:
1. You can enter the path to your map file by dragging it onto terminal, so you can enter cd<space> and then just drag the folder where your map is located onto the terminal window. Then hit Return (in the Terminal).
2. I'm not sure whether the names of the compiler tools in the above description are accurate. They might be different.
3. You can download Mac versions of the compiler tools from http://disenchant.net 

Funny, I've really searched many different help sites, but none said anything about putting map and utils in the same folder... the Mac utils still don't work, however (I'm on 10.6, maybe wrong version), so I'll have to stick to windows.
Thanks a lot, guys :) 

I hope I don't bother you guys too much with my questions, but since there's not much help available I'm pretty much forced to ask people around. I've noticed the Create Brush Entity/Trigger/Teleport and the Teleport Destination entity, but I don't know how to make them work :/
Still, I am quite happy I got to the point where Quake finally recognizes my map :D
Thank you! 

I forgot to explain that I'm trying to make a teleport, and that's what I need help with ;) 

Two things - the trigger area, which can be any brush, usually painted with a 'trigger' texture so you know what it is at a glance.

Turn that into an entity 'trigger_teleport' and make a info_teleport_destination.

Call the target of the trigger and the targetname of the destination the same thing, it doesn't matter what as long as they're the same.

"my_first_teleporter" or whatever :)

And it'll work. Problem is you won't be able to see the trigger in game - you'll just vanish and reappear at the destination when touching its area.

So you can include another brush there with the starfield texture which will make it a liquid volume, and look like the teleporters in the original maps.

Final thing to remember - all triggers are rectangles, if you include more brushes inside then they will just draw a big box over the top encompassing all of it to make a box.

In other words, prism trigger shape = rectange trigger volume. 

Hooray! Man, I love this feeling :D
However, two issues showed up. The powerups (quad damage and invisibility) don't work. I only used drag&drop, do they need extra attention? The other thing are messed up textures, like when you enter void with noclip. Can it be caused by a leak I've overlooked or something? The map is basically a box with flying ledges connected with stairs and bridges, maybe the box is too big?
Thanks again, I'm having wonderful fun :D 

My guess is that the powerups have fallen out of the level. In game, enter "developer 1" in the console before running your map and you should get a message telling you when they fall out. If so, try placing them a bit higher up - you want to avoid them intersecting the floor. 

Should just work without anything else needed. Not sure what's going on there.

The second issue sounds like the HOM or Hall of Mirrors effect. That means you've got some weird brushes that are making the vis process break.

Look for stuff that's very small. Try not to get smaller than 8 units unless it's for something that's also a func_door, func_wall or whatever.