When you log in for the first time, or from a new computer or browser, we will ask you for a PIN. This is because we use two factor authentications (if you really want to read up on it, you can take a look at the Wikipedia entry). Basically we want to make sure that you are who you say you are, so we send you a one-time password.
When we ask for a PIN, you will receive an email from email@example.com which contains the PIN. Just open up the email, grab the PIN (it's probably easiest to just copy and paste it), and enter it into the PIN pop up box. Now you're in.
We don't recommend turning off PIN security, but you are able to turn it off for individual users. Just log in as an administrator, open the User Tab, select the appropriate User, hit Disable PIN Security, and then save your changes.
For a refresher on Using the Administrator Role check out our video titled, Introduction to the Administrator Role .