There’s a lot of folklore in the Debian community about how apt works.
Unfortunately, a lot of it is also just plain wrong. For instance, I
often hear people confidently say things like aptitude is a
frontend to apt-get
(it isn’t).

These misconceptions are understandable — all the programs that use
apt perform the same tasks, many of them imitate each other’s
interfaces, and they all share common code. It’s easy to assume that
they must all be invoking apt-get under the hood. In the interest of
clearing up some of this confusion, I’ve created some simple diagrams
of what uses what in the apt system. apt is large and complicated, so
these diagrams can’t be complete, but I hope they at least clear up
the basic relationships between the different pieces of software.

This diagram shows how apt, dpkg, and some popular frontends are
related to one another (also available as a

Simple apt diagram

read more HERE