Step 1: First get the software.
Step 2: Setting yourself as an op
To be able to use console commands, you need to set yourself as an "op" (operator(I think)). To do this, put the Minecraft_Server.exe program into it's own folder, and run it. Once it displays "Done!", you can close it. You will notice that there are more files in that folder. Open the text file "ops.txt", and type your Minecraft username. (Josh1324, Notch, ect.) For each new "op" you add, you need to put it on a new line.
Step 3: Editing the settings on your server
"spawn-monsters=false" to "spawn-monsters=true". Besides that, there wont be really anything else you will do here.