What the hell, I'll be redundant.
Here's how to make a .pk3 file with Winzip if you have no custom content in your map (i.e. textures, sounds, or shaders you've made or downloaded seperately yourself).
Make a folder that has your map's name ("map-aggressor-wfa" for example). You can actually name it whatever you want but name it after your map to keep things organized. Or don't :P
In this folder, creat a folder called "maps" and a folder called "levelshots" and a folder called "scripts".
Place your .bsp file in "maps", your .jpg screenshot that displays on leveload in "levelshots" and a text file called yourmapname.arena (aggressor.arena for example) in "scripts". Make sure it's saved with the .arena extension. If you have any shaders that you have created (it's hard to avoid having to use your own), place those in the "scripts" folder also.
In this yourmapname.arena text file, paste this in and change the name to referance your map name:
{
map "yourmapname-wfa"
longname "Long Version of Your Map Name"
type "ctf"
}
Keep the quotes in the above example, btw.
Now select the "maps", "scripts", and "levelshots" folders all at once and right click on them. You'll see a Winzip menu with some options for different Winzip actions you can do. Choose "Add to Zip file.." and when the window pops up, hit New and navigate to your desktop. Type in the name of your map (map-aggressor-wfa for example ;) and save it as a zip file. Now go to your Desktop and remove the .zip extension from that file and replace it with .pk3. Zip the .pk3 up and throw in a readme and spam Rav and v3.
Open up other wfa maps with winzip and see how their .arena files are set up and check out some maps that have custom content to see how to do that, too. It'll make sense after doing a .pk3 with no custom content. A .pk3 file basically emulates your mapping baseq3 folder's file structure.