Step 1: Go to this thread( http://ugx-mods.com/forum/index.php/topic,4221.0.html ) and make sure to read everything before you download!
Step 2: Extract it to where you see fit.
Step 3: Tick these options (Fill in where it says (mapname) with your mapname

Step 4: Click Generate

First off open up radient. If you don't know how here is how you do it!
Step 1:Go to your Root folder (Either C:/Program Files (x86)/Steam/steamapps/common/Call Of Duty World At War/ Or C:/Program Files/Activision/Call Of Duty World At War )
Step 2: Navigate too your bin folder and open up the launcher

Step 3: Click on radient when the launcher starts up.

So you will see radient. It will look something like this when you first start it up:

Lets tidy that up.
Step 1: Drag that console (Thing the box full of text at the bottom) all the way down. It is unnecessary for what we want to do.
Step 2: Make the 3d (Big Box filled with gray on the left) view a little bigger but just enough so you have space too work with the 2d view (Grid on the left)
Step 3: Bring the texture list down but enough so you can see it. (Box full of pictures and names at the bottom left)
In the end your radient should look like this:


Step 4: Click File, Open and Then your mapname


Little Disclaimer:
All Of these images wont show the tasks but I had Gyazo wouldn't let me take screenshots with Ctrl -> Shift -> C

Step 1: Press Ctrl -> Tab till at the top left of your 2d view says this

This is the X Y View (Top down)
Step 2: Press 7 on your keyboard.
Step 3: Zoom out till it looks something like this

Step 4: Move the 2d view camera till it's in the center (Right click)
Step 5:Click on textures on the top bar

Step 6: Click Usage then tools

Step 7: Scroll down in the texture list and look for a texture (Image) called "Caulk" and click it!

Step 1: Start by making an Floor (left click)

Step 2: Resize to perfection (Left click at the sides) (Perfection, in this case, is an 8x8 box)

Step 3: Press Ctrl -> Tab to change to the X Z View (Front)

Step 4: Press 4 on your keyboard and make it 1 box long (Zoom in too see the smaller Boxes)

Step 5: Click the Floor in the center and move it one box down

Step 1: Press 7 on your keyboard
Step 2: Staying in X Z View, Create a wall with left click (Zoom out if you need too) (2 blocks tall)

Step 3: Press Ctrl -> Tab Twice (Gonna simply refer to pressing Ctrl -> Tab By saying it like this "Switch to top down view" Or "Switch to Front View")
Step 4: Press 4 then resize it till it is one block wide

Step 5: Press space and place the second wall at the other side of the floor

Step 6: Press space and click the Z on the bar at the top, then just line it up with the other edge of the floor

Step 7: Do the same as Step 5
Step 8: Shift Click the Floor (Select) then press space, Change to Front view then Move it up.

Step 1: Click onto Textures, Usage, then Interior Wall.

Step 2: Scroll down in the texture list until you find one you like. For me its this one:

Step 3: Ctrl -> Shift -> Click The walls in 3d view (Right click and use your mouse to move around. Use Ctrl -> Shift -> Right click to look around. Ctrl -> Caps Lock -> And right click to Ascend/Descend. There's the basics of 3d movement for ya!)
Step 4: Click on that texture you liked.
Step 5: Click on Texture, Usage and then Ceiling. Find a texture you like. For me its this one:

Step 6: Ctrl -> Shift -> Click The Ceiling then click that texture you liked.
Step 7: Do the same as Step 4 + 5 But on step 4 instead of clicking Ceiling click Floor.