If this is a fresh install and you have selected the option "Set it up for me", you probably had to put your Atlassian Id and password to finish your installation. Please, try to use your Atlassian ID and password to login.
I'm afraid your question is unclear. If you are logged into JIRA, you can check your "profile" to see your user name (top right, near your avatar). If you are not logged in, you will need to ask an admin what your id is or use the "forgot" function to get your account reset by email.
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