So when you want to record your demo, go in console and type "record (demo name here)". So for instance, if I wanted to title my demo "hola", I would type it like this in console:
Spoiler
When you wish to stop recording, all you need to do is type "stop" in console (no demo name required, just "stop").
Once you recorded your demo, you should be able to find it in your tf folder. For those who don't know where that is located, this directory should tell you:
Spoiler
In your tf folder, you should find the name of the demo with the extention .dem at the end: Spoiler
Now when it comes to sending those demos, simply just take your demo file and upload it to a file sharing website. I personally like to use dropbox.
And just as a bonus, to play the demo you have been sent, drag the demo file into your tf folder, launch TF2, and type in console: playdemo (demo name (in my case: playdemo hola)).
And that about sums it up. Hopefully this will clear up some confusion. Thanks for reading and have a nice day!