Ok Bram, Quick guide. & If you won't allow a full version of fraps to be posted, please delete link so i don't get into trouble.
1] Download & Install Fraps.(If link is deleted pm me)
[Link Removed - Mod] (This is my dropbox & the version i use.)
2] Open Fraps to configure it, These are my settings.
(Other options should be left the same as you see in the screenshot, If Fraps lowers fps too much then set "Video Capture Settings" to record half size.)
3a] Open Assetto Corsa & go to replays, from there you can choose a section of the replay to record from. when you're ready to record press "F9" and the yellow numbers will change to red, when you want to stop recording press "F9" again.
3b] You can also use fraps to record gameplay directly, Just press "F9" to start recording & "F9" to stop.
4] When you have made a recording you will need to compress it as the Fraps video is pretty large, This is where this guide comes in.
http://hayasacrew.com/xenforo/index.php?threads/converting-fraps.54/
5] When you've followed that guide you should be all set to upload much smaller files to Youtube.
If i'm not clear enough please ask me for more help.