You can reset your password if you have forgotten your password or have not been provided with one.
Steps
Go to the Sign In page: https://www.makerble.com/users/sign_in
Click the Forgot your password button
You arrive on the Forgotten Password page
Enter your email address into the box
Press the Send me reset password instructions button
You will receive an email with a link to reset your password
Open the email, click the link and reset your password
You will then be able to login and access Makerble