It's fundamentally more similar to American football than it seems, and they share an ancestral origin.
There are two kinds of Rugby;
Rugby Union
Rugby League
I'm a bigger fan of Rugby League and this world cup is the Rugby League World cup (Though TBH I actually PLAYED more rugby union- due to going to catholic schools).
Rugby Union is more popular globally, and especially popular in New Zealand and South Africa. Also popular in England, Scotland, Wales, Ireland, Scotland, Argentina, Japan, Italy, France, Fiji, Samoa, Tonga, and at some level is played in over 110 countries. In Australia it is only played by private schools, usually rich people (myself an exception).
Rugby League is VERY popular in Australia, and pretty popular in Northern England, then kind of popular in New Zealand and the pacific islands due to professional players in Australia of that heritage being good at it. It is also played a bit in France, but it's really not that popular elsewhere. It is the number 1 sport in the small developing nation of Papua New Guinea, so that's something, lol.
In Australia it's a big deal, and has been the "main sport" of especially Queensland and NSW (including Sydney) since 1908. Where I'm from it kind of runs in your blood, and actually kind of goes hand in hand with pig dogging in a way. The map of pig dogging popularity and Rugby League popularity in Australia is the same. The parts of the country where they don't hunt pigs you will find they play "Aussie Rules", which is very gay, instead of rugby league.
In fact there are even videos of professional NRL players hunting pigs with dogs.
I still remember when one of the best players in the league, Jamie Lyons, famously quit at the height of his career purely because he wanted to do more pig dogging and couldn't do it in Sydney. He ended up coming back, and even went on to play in the English Superleague where they couldn't get enough of the story about him quitting to hunt pigs.
Lyon brings relish for hunting pigs to sudden death run with the BullsAnyway I digress...
Rugby League is arguably MORE like american football than Rugby Union. Like American Football it's kind of rugby union made simpler in a way (and more entertaining).
Rugby Union has no limit of "downs", and hypothetically could just flow non stop until half time. Rugby League has "6 tackles" in the same way American football has "4 downs", but you can't "move the chains" in Rugby League. You have 6 and that's it. After the 5th tackle teams typically kick, just as they punt or go for a field goal on the 4th down in american football, but in rugby league that kick is often an "attacking" kick, which is probably most analogous to a "hail mary" pass in football. They can "bomb" a kick up high and hope one of their athletic outside backs (akin to recievers) runs through and catches it, or they can do a grounded "grubber" kick through the defense that someone can run through and grab, or a little chip kick over the top, etc. If they are too far down their own defensive end they will just do a long kick similar to a punt to get better field position.
In the first couple of "downs" they will typically do "hit ups", which is just a short pass to a usually a big strong guy who just runs straight into the defensive line. This is similar to like "inside" running plays in the NFL. Later on they might pass it wide out to fast athletic guys. They always have to pass backwards (or like level to themselves at best) with what you would call a "lateral" in american football. All passing in Rugby (both types) are laterals, you can only "pass" forward like a QB by kicking. Even then the "reciever" of the kick has to be onside. So when the guy kicks the "reciever" has to actually be behind him and then he can run forward and chase down the ball.
In rugby you have "forwards" which are like "linemen", and then "backs" which are like quarterbacks, running backs and recievers on offense, and like linebackers, cornerbacks and safeties on defense. But in Rugby (both kinds) everyone is both an offensive and a defensive player.
Rugby league has 13 on-field players per team, Rugby union has 15, and American football of course has 11. The field is a little wider and bigger in rugby. It is 100 metres as opposed to 100 yards between "end zones". 100 metres is about 110 yards. NFL gridirons are only 160 feet wide but rugby fields are actually 229 feet wide. So the extra players have some room. On the other hand there is no "blocking" in rugby, that is called an "obstruction" or "shepherding" and will be penalised. They have to find space to get through the defense by using their "lateral" passes and attacking kicks in tricky ways, and by ofcourse breaking tackles and making defenders miss with "juking and trucking" like in the NFL. When you want to score a "touch down" (called a "try" in rugby, which even I agree is confusing since it is not an attempt, but a success) you can't just "break the plane", you have to force the ball down on the grass in the end-zone with your hand.
Games have two 40 minute halves, and even though rugby league "stops" after each tackle it is very briefly compared to the NFL. A tackled player simply stands up and rolls the ball through his legs to a "dummy half" who then passes it to other playmaker positions. The defense has to take it upon themselves to retreat 10 metres after each tackle.
Dummy half, half back, five eighth and fullback are all kind of like "quarterbacks" in a way. And this suite of players are called "the spine" because of how important they are. Especially the Dummy half, HB and 5/8. The fullback traditionally was more like a safety/reciever but in recent years they have become instrumental in playmaking as well.
Forwards are big brutes, like line men, and they mostly act as battering rams and tackling machines, but even they have become more skilful and some are known for their playmaking.
I was a "flanker" in rugby union, flankers are actually the two extra players that are in union and not in league. They are forwards but on the smaller and more nimble side and it is their job to be out on the edge of the forwards to tackle sneaky guys trying to slip past the forward defenders, or to run off the shoulders of attacking forwards and receive hand-offs. On defense it's kind of equivalent to an outside linebacker I guess, and on offense like a running back that usually goes inside.
In rugby league I sometimes was a forward (2nd row) and sometimes was a back (centre), but I only played a small amount of league, because like I said I went to schools where they played rugby union.
This has kind of been a bit all over the place but hope you get the idea.
Here's some highlights from my all time favourite Rugby League player. He was a back, usually a Fullback or Centre (sometimes a wing, was even a 5/8th for a short time) so equivalent to a reciever, running back, corner or safety (or QB for 5/8). But yeah he was 6'4" 238 lbs, so a bit of a beast.
Biggest hits-
Scoring tries-
Representing my state (QLD)-
I started watching him playing local club football when he was a skinny teenager, and I was like "holy shit this guy is good", and sure enough he went on to be an all time goat legendary player.
