Go to the member's profile (click on their name from a posting they did), go to the options box under their picture, and select add as a friend.
If the member hasn't posted and you need to find them first, then
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go to the discussion topics link
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select a topic and post
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click on view all users under shortcuts
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type person's screen name
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click on their picture to go to their profile
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under options select "Add ______________ as a friend"
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type note and then submit request