Trying to learn all about karate to help my son
Gedan bari, the low block; gyaku zuki, the middle punch; and ura ken is the backfist. I agree with the other answers that these are basic techniques.
For a young child, such as your son, that's probably enough reason for him. But for you, that's not the whole picture.
They are not "only" a low block, punch, and backfist. These techniques also form a basis for a large number of applications - oyo.
Stated another way: suppose you're a chef, and 99% of your recipes call for salt. Most recipes call for it because of its flavor enhancement. Some call for different kinds of salt (like kosher, fine, table), because each has a particular physical property that gives it purpose. Some call for it for presentation (like kosher, rock, or pink salt). Others call for it because of its perceived health benefits (like sea salt). And chefs know that fires can be extinguished with salt. Many people don't know this, but table salt is nearly twice as dense as kosher, so, if using kosher as a substitute, you need to double the call. Would you agree, then, that salt is a basic spice you should have in your kitchen, and that you ought to know as much about it as possible so that you know how and when to use it?
Well, so it is with basic techniques, like gedanbari. We tell people that it's a block and protects the lower part of the body. Other instructors say it's basic because it's easy to execute.
Well, not really on both counts.
For example, most of the time, a strike to the lower body will be a kick or a weapon. What do you think will happen with that low block when used against a kick or bat? (yeah, - a trip to the hospital for a broken arm). Most of the time when we see it in kata, we always seem to be in some sort of long front stance. When was the last time you ever saw a fight (youtube, high school, pay-per-view...) that someone blocked something whilst in a front stance?
Maybe the low block isn't meant to be a low block.
And therein lies the secret in all of Karate: it's no block at all. (Well, it can be used as one. But it has many other purposes as well). The technique appears in so many kata because there are so many oyo - things you extract from a given technique. It is a block. It is also a strike. It is a vertical armbar. It is a wrist grab to release from a shoulder/lapel/neck grab. It is a lead to the front from a rear grab. It can be used as a hook for catching a kick or weapon. It's a slicing motion with a ken or tanto (or stick or knife). It's about several dozen other things that don't even have a name.
The low block to a karate-ka is like the salt to a chef: a most important and basic staple with many uses. As such, it's constant appearance in kata suggests the student ought to pay attention to every nuance about its execution: the feet, the hips, the torso, the head, the eyes, the other hand, the breathing... everything.
Reverse punch: it, too, is not just a punch. It can be used to distract, off balance (grab), strike, break, or lead in a throw.
Uraken: I wouldn't say this is a "most basic" technique. But it certainly has many oyo. The uraken is a backfist, and like a punch, can be used for similar oyo. The backfist can also represent some of the gedanbari bunkai as well. How do you throw a basic backfist? You hold your fist over your opposite shoulder, and then swing outward, yes? Well, you could also be grabbing a wrist who's grabbing at your shoulder, lapel, neck, hair, or ears; that outward swing can expose his midsection for you to implement another technique.
Learning all about Karate to help your son is a noble cause. I suggest, though, that you would learn a world more by taking your own classes. First, because it's a great way to bond with him. (Well, when in kumite, it's also a way to get back at him for talking back to you... :-)
You should also pick up a book (or two, or a dozen) on the subject. Learning history, organizations, biographies, and maybe a few helpful hints here and there is all an amazing way to develop talent and interest.
In some styles, for example Kyokushin, they form the most basic kata and kumite.
Kihon kata is formed by gedan barai and gyaku tzuki. Is required at 9kyu exam.
Uraken tzuki is useful in one of the kihon kumite. I dont remember details maybe it was for 7kyu exam. When I started training, my fist configuration during applying this technique was wrong and I needed some time to learn it properly.