Your login name for Office 365 is in this format:
Note that username is your network login, which is likely your last name and first initial, or just your last name. Examples: SmithA, DoeJ, Dickey
Your password is the same that you use for the network login, the one you use to login to the computer each day. In the Outlook Web Access site linked here, the Options menu allows a password change. Changing the password here will also change the password for your network account, website, and other linked accounts.