use of $block->content in custom php content

when using the custom php content pane, all the output is displayed above the header. i assume the initial help text in the body, 'Any content you want to have passed along to theme function for displaying MUST be stored in $block->content.' is the explanation but i have not a clue how to use that object. i would like the output displayed in the pane it was created obviously, any example code to give me a start? thx