This will be a quick guide, as it not as hard as it sounds to submit a demo.

Here is a video posted by NISLT/SiN for you to watch. My guide is just a typed, shorter version of the video.

First things you want to do is open your options, click advanced, and enable developer console if you havent done so before. Then when you want to record something, join a server, open the console using the ~ key. Once open type "record (yourdemoname)".

Once you have started recording, just play the game normal for as long as you want until something you want to submit happens.

When you got what you wanted open the console with ~ and type "stop". You will have then stopped recording. Once stopped, open the console again and type "playdemo (yourdemoname)" to watch your demo. Once you do that, your demo clip will start playing on your screen. While its playing, open the console and type "demoui". A small menu will open on screen.

Once the menu opens, you will see a small number counting up to a certian point. Thats the tick. When you see what you want to submit happen, copy the tick number a little before your part starts so that you have a little part before your part starts.

To find your demo, go to Program Files (x86)/Steam/SteamApps/common/Team Fortress 2/tf and look for yourdeoname.dem and rename it. You want to remane it using this template "HowToTitle_nick_tick_country.dem"

Once you rename it, all you have to do is send the file to nys2k12@gmail.com and hope it gets in an episode. Good Luck :D