There are two rings on the lens; Zoom Ring (Large/Wider ring) and Focus Ring (smaller ring). There is a switch on the side of the lens for Focus and Stabilizer. If the lens is a professional, it has a red band around the lens (indication of the Professional lens) in which the focus ring can be turned even if the focus switch is on AUTO MODE.
The Gold band around the lens means is ultrasonic, it has a better mechanism and probably better lens than one with a silver band lenses. These lenses focus ring should not be touch if focus switch is on automatic setting. Doing so will damage focusing mechanism unless otherwise indicated on your canon's manual.
NOTE: The lens zoom will not retract by it self because it is manual. It does not have automatic zoom so whatever position you use it last then that how it set when you turn the camera off. The only thing that might retract or extract is the focusing ring unless the lens has an internal focusing system.
Pro Lens is distinguish by the red band near the front of the lens.http://usa.canon.com/cusa/professional/products/lenses/ef_lens_lineup/lens_uw_pro/ef_16_35mm_f_2_8l_ii_usmhttp://www.canon.com/bctv/faq/if.html
If for some reason the camera is not focusing when the focusing switch is on AUTO MODE then it is possible that the lens focusing mechanism is damage.