Marie, that type of knife is known as a "stockman", in other words, a cattleman's knife. It is a standard and very popular style, because compact and convenient as it is to carry, it has three very different blades for different purposes.
Typically, the large blade, known as a clip point, would be used for general purpose cutting. The smaller blade next to it is the sheepsfoot, with a (rounded) safety tip. It could be kept with a heavy duty edge, for cutting hard or coarse materials, like rope. The third blade, off by itself at the butt of the knife, is a spey blade. This would be kept very sharp, and would be used for speying (or spaying), that is, castrating calves.
The knife you bought is well-worn, but looks like it has some life left in it! The age and the discolorations make it pretty certain that the blades are all high carbon steel, rather than stainless. This means they need some care, but will be strong and sharp.
If you mean for him to use it -- since it's not really collectible, but a working knife -- go ahead and clean it up and oil it. A simple way to start to clean it would be to get an ordinary eraser, and clean the blades with that. Keep your fingertips away from the edges! Then rub inside the handle with Q-tips with warm, soapy water, to get any gunk out. Then rinse it with cold water, blow it out, towel it out and off, and let it dry. Then lightly rub a little food-grade mineral oil on the blades with a folded paper towel, and rub some inside, too. Let it sit for a while, rub it dry again, and it should look pretty good.
Sharpening it is a whole different subject. Your dad may be up for that himself.
