Wifi network Linux-mint:
Press the network icon on the bottom bar and select your wireless network.
If no password is required, the connection will be established.
With password: see below.
Or in linux-mint Mate:
Click on network settings.
Click on the wheel(cog) of your wireless network:
Click the Security tab and enter your password. Check "show password" to make no mistakes.
Security type wpa & wpa2 personal is most commonly used. This depends on how the wireless router is set up. If no connection can be made, you can use a different security than wpa & wpa2 personal.
Then click on apply and close the windows.
Now go back to WiFi selection and click on your wireless network. These settings are remembered by the system even after a restart.