A primer, then.
Automatic fire is when the gun continues to fire, at a rate of about 10 shot per second, as long as you hold down the trigger, i.e., what most people think of as "machine gun."
Semi-automatic fire is one shot each time you pull the trigger. If you pull it as fast as you can, you'll get maybe 4 or 5 shots per second (won't hit much).
The "assault weapons" you see in the press and on TV are generally military designs made without the automatic fire option.
I'd say it's generally agreed that there is no practical civilian use for automatic fire. The argument over "assault weapons" is about capacity. Most assault rifles come standard with detachable magazines that hold 20-30 shots and can be replaced in a couple of seconds, and 50-75 shot "drums" are available for most models.
I have argued that there could be some beneficial effect from banning weapons that can accept a "detachable box magazine," i.e., the famous "clip" that allows "assault rifles (and some non-assault rifles" to be reloaded so quickly. It would also reduce the rate of fire of "automatic pistols" (confusingly enough, "automatic" in pistols means the same thing as "semi-automatic" in rifles). In other words, limiting civilians to weapons that can fire up to 10 shots (the number varies between 5 and 10) and take 5-20 seconds to reload. Slowing the rate of fire gives the potential victim, either of an individual shooting or a mass shooting, a better chance to flee or attack the shooter. Limiting capacity also favors the better shooter, if both are armed, in other words the "law-abiding citizen" who spends time at the range practicing, over the stereotypical gang banger.
As far as I'm concerned, the only "gun control" that would have meaningful effect (and would by no means reduce gun killings to, or anywhere near, zero) would be to ban the high-capacity weapons, leaving "law-abiding citizens" with revolvers and various types of rifles, including all of the semi-automatic "battle rifles" of WWII, hunting rifles (most of which are what we call "bolt action,") and lever-action rifles (the classic cowboy rifles). The latter two categories require an action, usually taking several seconds (though an expert can cut that to one second) after firing to ready the gun to fire again. That and limiting the amount of ammunition one can possess could have some beneficial effect. Whether or not it is worth it is open to debate, however, I am willing to state categorically that there is no legitimate civilian use for a weapon that fires more than ten shots without reloading.
As a friend of mine who loves revolvers says "If you need more than six shots, you need more than a handgun." Or as I sometimes put it "If you've fired six shots and you still have a problem, you need to put the gun down because you're a lousy shot."
