If this isn't made obvious by the the previous answers:

:bd will close the current buffer. If you don't want to grab the buffer list.

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

Use:

• :ls - to list buffers
• :bd#n - to close buffer where #n is the buffer number (use ls to get it)

Examples:

• to delete buffer 2:

  :bd2
  

Close buffer without closing the window

If you want to close a buffer without destroying your window layout (current layout based on splits), you can use a Plugin like bbye. Based on this, you can just use

:Bdelete (instead of :bdelete)
:Bwipeout (instead of :bwipeout)

Or just create a mapping in your .vimrc for easier access like

:nnoremap <Leader>q :Bdelete<CR>

Advantage over vim's :bdelete and :bwipeout

From the plugin's documentation:

• Close and remove the buffer.
• Show another file in that window.
• Show an empty file if you've got no other files open.
• Do not leave useless [no file] buffers if you decide to edit another file in that window.
• Work even if a file's open in multiple windows.
• Work a-okay with various buffer explorers and tabbars.

:bdelete vs :bwipeout

From the plugin's documentation:

Vim has two commands for closing a buffer: :bdelete and :bwipeout. The former removes the file from the buffer list, clears its options, variables and mappings. However, it remains in the jumplist, so Ctrl-o takes you back and reopens the file. If that's not what you want, use :bwipeout or Bbye's equivalent :Bwipeout where you would've used :bdelete.

How about

vim -O a a

That way you can edit a single file on your left and navigate the whole dir on your right... Just a thought, not the solution...