Check your buffer id using :buffers
you will see list of buffers there like
1 a.php
2 b.php
3 c.php
if you want to remove b.php from buffer
:2bw
if you want to remove/close all from buffers
:1,3bw
gt and gT switch
tabs back and forth
:q closes
only the current tab
:qa closes
everything and exits
:tabo closes
everything but the current tab