You have two choices: If you know HTML, you can add any tags you wish including images or links ito the description.
If you don't, you can choose to use an HTML editor in the description entry box (set this in Configuration > My Store > HTML Editor.) This will give you the ability to do some styling.

If you know CSS, you can use id and class tags in the description and style those in your stylesheet, making individual descriptions simpler to write.

It is also possible to change the product info page layout to almost anything you can imagine. Some of the changes are very simple and others are more complex to do.