I can understand how you might be confused by our differing levels of ATC service, but I find not knowing the difference between a PAR and an SRE (SRA) is baffling!
PAR: Precision Approach Radar. The controllers can see your azimuth and elevation on radar and will give correcting instructions to keep you on the 'glideslope' and 'localiser'.
Example: 'Right of the centerline, turn left 2 degrees heading 268 degrees. Slightly above the glideslope, correcting nicely'.
SRE: Surviellance Radar Equipment. The controller can see your position in azimuth, but not your elevation. They will give you correcting turns as above, and will offer information on what you height should be as you continue the approach.
Example: 'Left of the centreline, turn right 3 degrees heading 023 degrees. Height (or altitude) passing 1250 feet'. (This is the height/altitude you should be passing, not what you are actually at - remember, they can't see your elevation).
Given the option, take the PAR every time (unless you want the practice). As it's name suggests, the PAR is a precision approach and will often take you down to 200' AGL. The SRE is a Non Precision Approach and will be a higher minimum.
Regarding the ATC services available, PM me your email address and I will send you a power point presentation which describes the different services. It is not a formal document, but I have found it accurate.