How can I get alerted when there is a problem with my website?

You can get alerted that there is a problem with your website by adding your contact information (such as an e-mail address or your phone number) to "My Contacts" page ("Reporting" section).
The next step is to assign your contact to monitoring checks you created. You can do it at the end of the page, where you create and edit monitoring checks. Alternatively, you can also edit your contact information there.