When your administrator adds you to their My Hours account, you should receive an invitation email in your mailbox. Please follow the link in the message and set up your password. Then you will be able to log in.
In case the link expired before you managed to set a password, please ask your administrator to resend it.
Please, do not sign up on your own (without the invitation email) because this will create a new account, which will not be connected to your company. If you have already created a separate account, you need to close it before you can be added as a user to the company account.