EXPLAIN TLS/SSL IN SIMPLE TERMS (using simple paper mails and envelopes, simple physical addresses, bob and mary as recipients)

I am looking for someone to explain TLS/SSL in simple terms using a metaphor involving paper mails and envelopes, physical addresses, and recipients named Bob and Mary. The explanation should be suitable for a beginner's level of understanding.

you can do it by skype, whatsapp, telegram or any other means possible (probably phonecall will be needed), or just by writing (typing) the terms (probably this will not be enough though).