1. Log on to the Internet and check your email account for any email from 'Google' or 'Google AdSense' specifically. Also check your email's spam folder for any possible missed emails from Google that will give you an update on the status of your Google AdSense application. The email from Google Adsense will contain either a letter of acceptance as well as login instructions or a letter of denial along with the reason why.
2. Log in to Google AdSense (google.com/adsense) using the email address and password you used when you applied to see if you are registered within the system. If you cannot access your account, it does not mean you were automatically rejected --- it may take additional time to add your name into Google AdSense's system. If you can successfully access your account and land on the AdSense user dashboard, your account is active and ready for use.
3. Contact Google AdSense by accessing the official Google Adsense website (google.com/adsense) if you have waited longer than you were told when you initially applied. Although you may not receive a response immediately, Google may be able to direct you in a direction to find the status of your application individually.