Connect your Mac to the Internet using Wi-Fi
If you’re within range of a Wi-Fi network, you can try to join it.
Join a public Wi-Fi network
On your Mac, click the Wi-Fi icon
in the menu bar, then choose the network you want to join.If you don’t see the Wi-Fi icon
in the menu bar, choose Apple menu 
> System Preferences, click Network, select Wi-Fi, then select “Show Wi-Fi status in menu bar.”If requested, enter the password for the network, then click Join.
Join a hidden Wi-Fi network
You need to know the hidden network’s name, security protocol, and password to join it.
On your Mac, click the Wi-Fi icon
in the menu bar, then choose Join Other Network.If you don’t see the Wi-Fi icon
in the menu bar, choose Apple menu > System Preferences, click Network, select Wi-Fi, then select “Show Wi-Fi status in menu bar.”Click the Security pop-up menu, then choose the type of wireless security.
Enter the information for any additional fields that are displayed, then click Join.