You normally send a short message which contains twenty-five words or less to the creature by you’re familiar. Actually the specific creature hears the message in its mind and easily recognizes you like a sender when it knows you, and even can able to answer in a like manner as soon as possible. So the spell will enable the creatures with intelligence scores of at least 1 to understand the meaning of your actual message.
No matter how much distance would like to send a message, you can easily send a message through out any distance and of course to other planes of existence, but sometimes if the target is one a different plane than you and there is a 5% of chances which the message does not arrive.
You may also like to read about commune 5e spell
Attributes Of DnD 5E Sending
|Casting Time||1 action|
|Classes||Bard, Cleric, Wizard|
|Components||V S M|
|Material||A short piece of fine copper wire|
|Target||A creature with which you are familiar|