You just have to download the software here :
=>
https://www.teamviewer.com
Double-click once the download ends, install or run once only (choose according to your needs).
At the end of this process, you'll get the main interface of the app and you just have to put the 9 digits in the "Partner ID" text area (most of the time, you'll have to check the "remote control" radio button below, most partners don't allow file transfer).
Click "Connect to partner" and if the guy is still online, you'll have to put the password as requested (you'll see people give two infos : 9 digits = ID, the rest = password).
Hope this helps
