BuddyPress.org

jjj is correct. If you are working on BP theme customizations, you can often find a template tag to grab and output the data. That will always be the best approach.

But if you are creating your own plugin–as I am assuming based on the title of your thread–then you must make sure that the data you are manipulating in your various functions is made available to a given function’s logic. This can sometimes be done by passing the data via paramaters. But, sometimes the simplest approach is to redeclare a varibable in that function with global.

I can’t get anything to show up with <?php bp_user_fullname() ?> and $bp in global.

Try this:

<?php echo bp_user_fullname() ?>