B5: How to identify an atom.

There are two ways to identify an atom. The easiest way is to simply click the Left Mouse button on the atom. The atom name and residue to which it belongs should appear in the very bottom of your browser window (the "window status line"):

If you want to permanently label an atom, you can do so by following this series of commands with the menu: Select¬Mouse Click Action¬Toggle Atom Label. The menus that were selected should appear as shown to the left. After you have completed the selection you can use the mouse to click on an atom to label it. Once you have finished labeling the atom(s), you probably want to restore the mouse action to just identifying the atom (the default mode) by the following series of commands: Select¬Mouse Click Action¬Identify.

What do the Labels Mean?

The labels that appear in the status bar (or on the image) refer to the particular atom that was selected. Considering the following example:
Atom CB 371 Group: ALA 48
          | The beta-carbon was selected
                | It is atom number 371 in the coordinate file.
                                    | It is contained in an Ala residue
                                            | Which is residue 48 in the protein

If the structure contains more than one chain (Look at the U1A example), then the chain to which the atom belongs is also shown:
Atom CB 371 Group: ALA 48 Chain A
                                                | The atom is found on Chain A