In your template where you see
the_title(), you will want to change it to something along the following:
echo get_the_title() . ', ' .
'posted by ' .
get_the_author() . ', ' .
human_time_diff( get_the_time( 'U' ), current_time( 'timestamp' ) ) .
human_time_diff() is the one doing the part regarding your topic. Though you also asked for the others.
However, if you want it to look even cleaner, try:
'<h2>%s, posted by %s, %s ago</h2>',
get_the_time( 'U' ),
current_time( 'timestamp' )
Replacing whatever tag/formatting you want in the first parameter