On cell phones there is a way of sending short (160 character) messages between two cell phones. Commonly this is known as texting, the technical name for this is SMS (Short Message Service).
SMS is quiet, fast and efficient, originally more popular in Europe, it caught on in the USA. Many cell phone users use SMS rather than voice calls.
SMS messages are "In the clear", meaning the message and its meta-data can be easily read by a third party. There is a solution, you can load Signal on your smart phone (iPhone and Android). It will integrate with your phone's regular SMS app.
When you text to another user of Signal, your message will be encrypted. Your phone will confirm this with a padlock icon on the message received from another user of Signal and when you message another Signal user you will see a padlock icon and a double check (tick) indicating that your message was received encrypted.
But that's not all!
When you have Signal installed you can also make encrypted phone calls to another user who has Signal installed. So now you can make a call that can not be eavesdropped on. At the top of the text page for the other Signal user, you will see a phone icon. Touch it and an encrypted call will be set up.
Signal uses the Internet to communicate, not the cell phone network. So, if a WiFi signal is available, Signal will use that, if not it will use the Cell provider's data network. Note that some public WiFi sites block ports and Signal will fail when trying to use such a WiFi system.
Installing Signal is very easy, you can load it on an Android via the Google Play Store app or on iPhone via iTunes. Once it is downloaded, you just start using it. It's that simple, it's that secure.
Signal is a product of Whisper Systems https://whispersystems.org/