There are a few reasons why you might not be seeing your formatting. The first thing to keep in mind is that you won't see the effects of your formatting until you export. The formatting is, currently, not visible in the editor.
If your formatting isn't appearing in your exported file, check to make sure that your opening and closing asterisks match. If, for example, you wrote **It was the best of times, it was the worst of times*, you would get exactly that in the export since the opening and closing asterisks don't match.
Line breaks (pressing enter) will also stop the formatting. If you write:
**Shall I compare thee to a summer's day?
Thou art more lovely and more temperate.**
That is what you will get. The return at the end of "day?" stops the formatting. You would need to write:
**Shall I compare thee to a summer's day?**
**Thou art more lovely and more temperate.**