Visit the site and click the login button in the top left corner, then choose 'forgot password' - you'll be emailed a link to reset your password, after which you can log straight in.
If you didn't set a password after signing up, you can always go to the login page (accessed by the 'login' button in the top left of every page) and choose 'forgot password'. You will be emailed a reset link.
Some email clients incorrectly flag WordPress email as spam - first place to check if an email doesn't arrive is your spam folder. You can always try resetting your password again, and if the email still doesn't come, please contact the site administrator who will reset it for you.
Please ensure that both the device you are using and the browser you are using are up to date, with no pending updates. If you still experience issues, it can be useful to clear the browser cache and/or reset your device. If issues still persist, contact the site admin with the device and browser versions so that we can take a deeper look.