Before you can start up Radiant you need to edit kingpin.qe4.
To locate youre kingpin.qe4 it depence where you installed Kingpin.
For default Kingpin installes Kingpin in C:\Program Files\Kingpin\
But for Kingpin steam it is: C:\Program Files\Steam\steamapps\common\kingpin\
But it also good posible that you installed Kingpin in:
C:\Games\Kingpin\ or somewhere else.
Somethimes is just better to install Kingpin 2 times becouse most of the time when you map you don't want all textures using that you already have download.
Also if you installed Kingpin in C:\Program Files\Kingpin you could get in problem when compiling a map.
So if you got for example got Kingpin installed in C:\Program Files\Steam\steamapps\common\kingpin\ you should go to the directory C:\Program Files\Steam\steamapps\common\kingpin\kprad\
And then open kingpin.qe4 with notepad.
Just right click with mouse on kingpin.qe4 and choose Open With... Notepad
It should look like this then:
You should change all the lines called C:\Progra~1\Kingpin\ and C:\Program Files\Kingpin\

Also when you installed Kingpin in C:\Program Files\Kingpin\ Becouse Radiant only can read 8 characters in directory's like in old dos.
So C:\Program Files\Kingpin\ becomes C:\Progra~1\Kingpin\ most of the time.

But becouse C:\Program Files\Steam\steamapps\common\kingpin\ is so very long it is better to replace the total text file with:
So it will showup like this:
But you also can change it manual if you want to experiment or download a other example fix here.[downloads.kingpinforever.com]
Or if you want more information about kingpin.qe4 you also could read Hypov8 Tutorial.[www.kingpinforever.com]

Becouse kingpin.def that is installed in youre Kingpin\kprad directory is a bit old.
And i bet you also want to use new things that are not in the old kingpin.def file like for example the Heavy Machine Gun Cooler.
You need a new one.
To download it click here kingpin.def.[downloads.kingpinforever.com]
Just unzip it in youre Kingpin\kprad\ directory.
And overwrite the kingpin.def file.

Now youre ready to start radiant.exe
Wats is in the same directory where you kingpinq.qe4 is Kingpin\kprad\.
When you start radiant.exe for the first time it would look up like this:
Just press the OK button

If you don't see that screen and still want to setup radiant.
Go to Edit|Preferences...

The next screen you would show up like this:
If you got Kingpin got installed in C:\Program Files\Kingpin\ you almost only have to press the OK button.
Most settings are setup good for default then.
But i assume that you got Kingpin got installed in
C:\Program Files\Steam\steamapps\common\kingpin\
You should change then "Game path / Tool settings / Stuff that wouldn't fit anywhere else" then from c:\program files\kingpin\kingpin.exe to C:\Program Files\Steam\steamapps\common\kingpin\Kingpin.exe.
Also you should change the "Use PAK file" directory from c:\program files\kingpin\main\pak0.pak to C:\Program Files\Steam\steamapps\common\kingpin\main\pak0.pak.
Maybe it's also usefull to change the "User INI path:" directory to this: C:\Program Files\Steam\steamapps\common\kingpin\kprad\radiant.ini or any other directory path where you installed kingpin.

I find "Auto save every 5 minutes" a bit to fast to save every 5 minutes a backup of youre map so i changed it to 30 minutes.
But you can change it to youre own settings wot you like to save.
Youre backups of map saving comes in the directory C:\Games\Kingpin\main\maps\snapshots\
Please note that those maps don't save maps as .map at then end so if youre map is called kpdm187.map it will save the first time as kpdm187.map.0 and then after that it saves again kpdm187.map.1 and so on etc.

Also at Mouse i put buttons to 2 buttons becouse i don't know wot 3 buttons do and i probably will never use and it would only would be annoying if i then accidentally press that button.

So after setting up QERadiant Preferences it would showup like this:
Youre now ready to press the OK button
It will now ask for the kingpin.qe4 that we have setup before.
Just click on the kingpin.qe4 (or the kingpin_fix5.qe4) and press the Open button.
Next it will ask to create a default project?
This is more needed if you are building a new mod so just press the No button.
Maybe i gone put a tutorial about that also but for now you don't need to learn that.

If you pressed Yes accidentally just press the Cancel button.

Radiant will now startup and will look like this:

This is optional becouse i don't like these colors and want the orginale Xatrix colors.
I go to Misc|Colors|Themes|Xatrix 1
Oke youre now all ready to start mapping for Kingpin.