What is the purpose of “&&” in a shell command?

Question

As per my knowledge using the & after the command is for running it in the background.

Example 

& usage: tar -czf file.tar.gz dirname &

But how about &&? 

Answer 1

Furthermore, you also have || which is the logical or, and also; which is just a separator that doesn't care what happened to the command before.

Oops, fail

$ true || echo "Will not be printed"

$  

$ true && echo "Things went well"

Things went well

$ false && echo "Will not be printed"

$

$ false ; echo "This will always run"

This will always run

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