There are a lot of encrypted and “secure” mobile chat/messaging apps out there. But the gold standard and perhaps best option is made by Open Whisper Systems called Signal. They developed the protocol that others like WhatsApp use for end-to-end encryption. The only reason I am not encouraging you to actually use WhatsApp is that they also opt’d people into data collection for their advertising efforts since they are owned by Facebook.
Along with messaging Signal allows for end-to-end encrypted phone calls.
If you use Chrome browser you can also install the browser plugin for Signal after you install the mobile app. Allowing you to message people from your desktop.