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The member list, accessed via the 'Members' link at the top of each page, is basically a listing of all of the members that have registered on the board.
If you are looking to search for a particular member by all/part of their username, then in the drop down box at the bottom of the page, change the selection from 'Search All Available' to 'Name Begins With' or 'Name Contains' and input all/part of their name in the text input field and press the 'Go!' button.
Also, at the bottom of the member list page, there are a number of sorting options available to alter the way in which the list is displayed.
If a member has chosen to add a photo to their profile information, then a camera icon will appear next to their name, and you may click this to view the photo.