From The Top
First, you will need a copy of CoD Radiant, which is the map editing program. This can be found at Call of Duty Filefront. Once downloaded, install the programs by opening CoDtools.exe. Once installed, go into your callofduty/main/maps folder and make a folder for your custom maps.
Setting Up
Open your editor, which will ask you to locate the cod.qu3 file, which should be in tools\\bin. Next, set up your preferences. From the Edit menu, click on Preferences. Here you can choose your layout, from which there are four options. Play around with the four layouts to decide which ones you like best. Many of the options here are exactly as the title implies: preferential.
You should unhide your texture tools by making sure the boxes next to the Texture Toolbar, the Texture Scroll bar and the Texture Subset are not checked. These will provide a useful toolbar and other features for managing your textures. Set the editor to auto-load the last project you worked on, or set it to auto-save every ̶0;x̶1; minutes, where you can define the value of ̶0;x.\" These and other options are available, so take some time to decide which ones you like best.
Your First Room
Start with a simple box room. Open a new document and start by creating the floor. Make a simple square on the interface grid to lay out the floor. Next, choose a texture for your floor from the window in the lower right of the interface. Textures come in sets and finding similar textures to ones you used already shouldn̵7;t be hard. Once a texture is chosen, hit Ctrl+Tab to auto configure your floor to game standard height and width. You now can place you floor down by hitting the space bar. Once it is placed, delete the object with the delete key, and move on to the walls.
Draw out you desired wall, texture it and place it, but don̵7;t delete it. Save time by copying this template to the four sides. Draw a ceiling, texture and place it as you did with the floor. Now, you have a box. Right-click on the main window and select light, and a light entity will appear. Affix the entity where you like, and you have a lighted box. From here, experiment a bit with different textures, angles and lights to create your battlefield masterpiece.