[SOLVED] how to run remote access

About 10 years ago when i had a pc on a service contract i rang a well know store and they put a box on screen and sent me an email with a code in , i then put the code into the box to trigger the remote access , they did this for legal reasons , because i put the code in i was agreeing to let them access my pc.

I now have a friend who has a fault on his pc and due to covid 19 i will have to help him by remote access but i dont know what i as the "helper" has to do access the other pc and i dont know what my friend has to do to let me access his pc.

MODERATORS..... if you think my question will breach your security rules i have no objection if you remove it.
 
Solution
Free tools will be limited but take a look at join me.
There are also a slew of paid apps like logmein, splashtop, teamviewer, gotomypc, zoho assist, etc.

Note that these remote softwares require Windows to be running.