Encryption is about making information private so that only authorised parties can view it. That's simple enough to understand because we all have information we want to keep private: conversations, banking details, financial information, private photographes, and more.
Obviously encryption goes beyond what we need as individuals. Organisations, private and public, need to use encryption too because we trust them with our information: medical, financial, and other sensitive information.
Encryption enables us all to conceal information from those not authorised to see it.
How is this achieved? Well there are a few ways, but we're going to over symmetric and asymmetric encryption as they're the most widely used methods in the world.