I've installed cs50 appliance as second OS on my notebook, but I cant turn on my WiFi - Fn+F3 doesn`t work( need some help from community, thanks)
Wifi on laptops with linux can be a bit tricky sometimes as there is a whole slew of things that could potentially be the problem.
First things first. You need to find out if the appliance even recognizes that there is a wireless nic. In a terminal:
This should provide a list of available interfaces. Wireless interfaces are often listed as 'wlanx' where x is some number. If there isn't a 'wlanx' then ubuntu isn't loading the module for your card. I would recommend taking a look at https://help.ubuntu.com/community/WifiDocs/WirelessTroubleShootingGuide. There they offer some advice on finding what type of card you have, locating drivers, etc.
If you're lucky, it might just be that there is a soft block on the wifi radio. In a terminal:
This should list the available interfaces and whether or not they have a soft or hard block. If it does indicate there is a soft block, you can clear it by doing:
rfkill unblock x
where x is the number to the far left of the wireless interface. Then reboot your computer.
I wish that I could be more help, but it's hard without more specifics. The link above is an excellent place to start. Let me know if there is anything else I can do.