Do you mean encryption of the wifi signal? If so, look at
wpa_supplicant and NetworkManager. Most public wifi hotspots
do not support encrypted wifi.
You can also encrypt the traffic going to and from an endpoint
using a VPN client. There are many, and you'd need to match
your software with the VPN that has been set up.
Other than this, you can use encrpyted protocols such as
https, imaps, ssh, scp, sftp and ftps. Avoid unecrypted
protocols such as http, imap, pop3 and ftp.