Not a dumb question at all.
All guns come standard with at least rudimentary sighting systems, some with slightly higher-performance systems, and some with fairly complicated systems.
The most basic system that all handguns come with will look like some (minor) variation of the picture that Wyldekard posted for you. In the most basic configuration, both the rear and front sights are machined or otherwise permanently hard-mounted to the frame/slide/barrel, meaning there's no adjustment available to the user.
A slightly higher-tech system will have the rear sight mounted by a "dovetail" notch machined into the frame (revolver) or slide (semi-auto like the XD you shot) so that it can be adjusted by tapping it with a drift and a small hammer side-to-side to adjust for windage.
The next higher-tech system is the rear sight having the ability to be adjusted by a screw. The basic adjustable sight will only have windage (horizontal) adjustment, and a slightly more functional one will have both windage and vertical adjustment.
From there, you can get standard sights that have glow-in-the-dark dots to aid in aligning your front and rear sights in low light.
When you hear terms like "red dot sights" or "holographic" or "reflex" sights, in almost every case, you're hearing about an add-on sighting system that would not come as a stock feature of your handgun. I've never looked into stats on which kinds of systems sell better, but there are two basic ways to mount a red dot sight, which when talking about a handgun for self defense purposes, you are usually referring to a laser sight. The two mounting systems are via an accessory rail built into the frame of the weapon, or via a system built into the grip of the weapon. The XD that you shot has a rail along the bottom of the frame, in front of the trigger guard. I personally like the rail system because it is more versatile than mounting the laser in the grip, but both can be very helpful in acquiring your target, especially for follow-up shots. They also can be a distraction for some people, especially for those, like a lot of us here, who are just so ummm.....ancient (LOL), that we are akin to trying to teach an old dog new tricks.
Anyway, here's a couple of pics of one of my guns that does have fully adjustable (windage and vertical) sights, night-sight dots, a rail that you can see in the first pic without anything attached, and in the second pic, with a combination flashlight and laser mounted on it.
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And here's one where you can see what the night-sights are designed to do. The pic is retouched to exaggerate the GID dots, but that's only because it was taken during the day and you couldn't tell they were night-sights if I didn't do that. In low-light, they would look similar to how they look here:
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Hope that helps. Keep asking questions. It will really help you when you go to buy a gun.
Blues