After you have submitted the registration form, you should get an email message that contains a link. The link is used for confirming your e-mail address. When you click the link, your motocaching account will be activated.
You should get the e-mail in a few minutes (in rare cases it has taken an hour due to technical issues with mail service provider).
Most common reasons for problems in registration are these two: 1) The confirmation email sent by motocaching.net ended up in the spam folder instead of inbox (please check your spam folder). 2) There was a typo in your email address and the email could not be sent to you.
Whatever the reason is, the result is that your account is not active and you can't login.
To activate your account: Go to the login page and click the 'Registration support' link and follow the instructions.