When should I cancel Amazon Prime?

I accidentally got Prime when ordering an Amazon package. I only noticed it today when I ordered something else and wanted to see when it would arrive. Then I saw that it was coming tomorrow and was confused. When I checked my emails, I noticed all the emails from Amazon. The second one said, "Welcome to Amazon Prime." The email also stated that I had a free trial month.

My question is, so that I don't have to pay anything at the end of the month but can still use it, should I cancel Amazon Prime now or wait until the 30 days are up?

And one more question: Can I use Audible during the 30 days or is that extra?

Thanks in advance for answers.