There are a lot of useful applications, such as WhatsApp, for secure messaging, voice, video and attachments. Some are free, some you pay for, some meet recognised standards and others make money from harvesting information about you.
Before deciding which application is most suitable, as they all have their place, carry out your own assessment starting with evaluating how important the information is to you. If you decide your information has zero value, then some encryption is better than none so go with a free application, however do so with the understanding it is free because the application/service is most likely going to use some or all of your information for their own purposes.
If your information does have a value, then look at something with product assurance and preferably independently tested by a third party.
More information is available from the National Cyber Security Centre or contact Serbus and we will be pleased to provide you with no-obligation advice.