Cryptocat can be used for secure chat communications. According to the EFF"s "Secure Messaging Scorecard," it is one of the most secure messaging programmes available (see https://www.eff.org/secure-messaging-scorecard). Both users have to install Cryptocat on their computers and then connect to the same encrypted conversation. It's crucial that you authenticate that the person you are chatting to is who they say they are, for example by telephone (Cryptocat alerts you to the need to authenticate.) To use Cryptocat, go to the Crytocat website (https://crypto.cat), install the add-on for your browser, go to the Cryptocat menu option (perhaps Tools > Cryptocat), type in a conversation name, type in your nickname, and click connect.