Not everything has to be complicated,
the most important thing is to have fun.

It is silly to try to learn with having fun,
it is actually where medical malpractice comes from.

Try as he might - and try not to ponder this too much,
but your doctor would fail all the medical quizzes and exams if he took them today.

And that's not even mentioning,
High School and College Exams.

So don’t be like your Doctor,
and learn for real.

Which is to say,
have fun.

Blender has a Sculpting Mode,
where you are presented with a Sphere you can sculpt.

You need to take a sculpting tutorial,
and learn about re-meshing or enabling dynamic topology.

And then a Blender Boolean Modifier tutorial,
to attach a loop for a chain.

And that is all the hard stuff,
because 3D printing does not require thinking about molds.

A 3D printer takes care of the inside area of your creation automatically,
it uses just enough filament to make your creation sturdy.

To make things easier,
you can model something with a tail looped in a loop.

For example a cat, that has a loop in a tail,
at that is how you would attach it to your chain.

You can model something that looks like,
it is hanging on to your key-chain as well.

A monkey, an octopus,
or a cheerful misshapen raccoon.

This lets you skip the whole Boolean modifier step,
so that you are printing a ready to hang pendant.

That is all there is too it,
it is easy to make pendants.

If you want a tiny challenge though,
strategise about your creatures so that not only do they not need a loop.

But they don’t need special mold considerations
when printing or casting in gold - this way you can make a complete jewelry piece.

Pendants are special,
because they don’t have sizes like rings or bracelets.

And don’t forget that earring are a kind of a pendant too,
as you learn more you will be able to decorate your rings with your creations too.

So once you finish a wireframe-like octopus,
or a flat creature, like a long cat relief pendant.

So as long as the octopus is hanging onto the chain,
or the kitty has a loop in its tail.

You upload it to your online-printing-service store front,
and you have both a gold jewelry piece for sale, and a new entry in your design portfolio.