How do customers get an account?

So I set up my very simple store and left the “My Account” link in the main menu (default). I sort of assumed that customers in my Storefront shop would have the opportunity to choose a password at checkout. A lot of people wrote to me saying they couldn’t setup an account and I encountered the same thing when I purchased something from my own store as a test! I then used that e-mail address (not the one I use to manage my account) to try the “lost password” process on the “My Account” page and nothing. Invalid username/email. So how do my customers actually get an account with my shop to be able to use the My Account feature to track orders, etc…?

Thanks in advance!
Deena

The page I need help with: [log in to see the link]