The Ranger is classified as a quarter ton pickup but may be rated for more or less payload. Your GVWR is on the doorframe and is the maximum loaded weight. Your available payload is the GVWR minus the weight of the truck. Either the sticker or your owner's manual will define what the GVWR of the truck is (ie, fully fueled, with one or two passengers, etc).
The question you asked is loaded because the GVWR will depend on options, etc and is what the manufacturer set it at.
The GVWR rating will tell you what the manufacturer said is the maximum weight of the truck and its load (in the bed / cab / whatever) but does not necessarily correlate to the safest weight you can handle. IE the GVWR is unsafe if your tires have 0 tread, or you drive like a douche.
Conversely, you can add modifications that make the truck safer, possibly even safer than a stock truck below its GVWR, at a given weight, but will not increase the GVWR. The GVWR is static unless you have it legally changed (I checked in to it, a PITA).
So all those words are a long way of saying that your truck will be safest when you are within your capabilities and the truck's capabilities.
Absent a scale, I'd just put shingles in the bed until it starts to squat and then dump the load
