How does data encryption help keep data secure?

When data is stored or sent, it can be sent as it is, when over a network this would be packets.

But when data is encrypted, its simply like saying, if i sent you an email that says

Hi, How are you

H = 103343

i = 408300

, = 985742

The numbers are sent not the letters so the computer on the other end, Decrypts this data for your display.