Alright, I'm going to try to go through some major things that you need to know. So, as you know, VGC is using two Pokemon. These Pokemon are facing another pair of two Pokemon. You make a team of 6, however, you're only allowed to bring four. To read more about specific mechanics, I would suggest reading this article. Ok, so now, I'm sure you know the basics. Here are a few general tips, before I start going more into depth into VGC.
First: Fake out is really good. Stopping a dangerous opposing threat, while enabling your possibly other dangerous Pokemon to do a lot of damage, or to even set up to destroy everything on the field. Second, Intimidate is one of the best abilities. Many metagames in VGC are physically dominant on the attacking side, so stopping those horrifying threats is almost essential to success.
The specific metagame going on right now
Ok, so now I'm going to talk about the specific metagame going on right now. So if you scroll through the pikalytics usage rates, which is linked here. The most common Pokemon....is incineroar, who, has intimidate! WOW! In all seriousness, the reason that incineroar has the most usage of all intimidators is interesting. It has a bevy of amazing support moves, such as fake out, parting shot, taunt and snarl. Now, the thing that makes parting shot so effective, as usually in singles, parting shot honestly isn't the best, is switching is NOT common in vgc. Of course, switching happens, however, because Pokemon in VGC are usually MUCH bulkier and just more direct threats, they usually don't like switching.
Anyways, next, we have Tapu fini. Tapu Fini is a good "wall", along with having the bulk to set up on things easily with calm mind. With that, you'd watch in horror as it murders your entire team. Fun. It also gets access to taunt, which is good in stopping a particularly annoying archetype, trick room, which we will talk about later with other team styles and cores. We also have Landorus therian, which, surprise, is another intimidator. It is much more offensively inclined 'mon, which sometimes doesn't even carry protect, which, by the way, is essential on almost all non assault vest.
Next, we have.....-_- Regieleki. This....thing is really annoying to handle with a modest transistor magnet boosted thunderbolt. It can rip through teams, and I've seen many....shall we say irate.....posts on Reddit getting mad about losing because their Regieleki lost a speed tie. Fun. It can even run screens, and because of this things OBSCENE speed, it can set up both. It can run light clay, or sash, or life orb, or magnet, and even because of its objectively horrible movepool, it is really versatile.
Next, we have rillaboom. Side note: I'm going to go through the 10 most common mons, and, when I talk about specific archetypes, other Pokemon WILL be mentioned. Anyways, ze monke that does much photosynthesis is a terrifying attacker for many reasons. This monke has pretty decent bulk. It has access to fake out, and it almost always it always using all attacking moves, making the assault vest the perfect choice for this monke terror. It can also carry miracle seed, taking this things grassy glide to murderous levels. Speaking of grassy glide, it gets a 70 base priority move. Now, at first glance, that's not that good. Here's the thing. It gets stab, so that's 105 base power. Pretty dang good. Now, here's where things get....insane. Lets say it's carrying miracle seed, which boosts grass moves by 20%. It is quite common, making an appearance 31% of the time. So, 105 * 1.2, which gets to 126. Now, this is starting to get obscene. HOWEVER, we aren't done yet. Grassy glide only works in grassy terrain, which rillaboom sets. Coincidentally, Grassy terrain boosts grass attacks by oh, only 50%. So, now, we have a 189 base power grass type priority move. Fun.
Anyways, next, we have porygon 2, a bulky trick room setter. With eviolite, it just.....survives. It can learn some annoying support moves in Ally switch and eerie impulse to screw single targeting foes, and eerie impulse to destroy dangerous special attackers.
Next, we have urshifu. There isn't anything else to say other than some really balanced stats, and guaranteed crits with wicked blow.
Next, we have grimmsnarl, which is a mon with prankster. Basically, you know what it's about to do. It uses screens, fake tears, thunder wave, the works. It can also use Spirit break to really annoy special attackers. Oh yeah, it also gets fake out.
Before the last mon, we have glastrier. Glastrier is a horrifying trick room murderer with....hmmm...145 attack. Yeah pretty chill. It also has 130 and 110 defenses and has amazing coverage. Yeah, pretty balanced, I must say. Oh, and one more interesting thing. Ice is a horrible defensive typing, so weakness policy activates very easily. Fun.
Finally, we have the unloved koala brother. Urshifu-R. This boi has an interesting niche of being able to deal huge damage, while also breaking sashes because it has a multi hit move.
So, let's finally talk about some strategies. I'm going to go through some fun archetypes. First, Trick room. Trick room is quite simple. Get a bunch of slow, heavy hitters, and reak havoc while your fast opponents are suddenly the slowest Pokemon and you kill. Pretty simple. You need a setter, a redirector, like amoongus, which redirects attacks to itself, and an absuser, or something that likes to kill. Trick room is a dangerous archetype.
The next one I'm going to talk about are Beat up Teams. Basically, this uses justified, which boosts attack by one stage if the mon is hit by a dark type move, and a Pokemon that uses beat up, which hits the amount of times of the 'mons in battle. So basically, you've got a 'mon that's getting to a *3 multiplier. Then it kills stuff.
Finally, the last archetype that I'm going to talk about is WP Coalossal. Coalossal is interesting. It has an ability which boosts speed by 3 stages when hit by a water and fire move. With a water move, it can utilize weakness policy too. Now, the thing that makes it so effective is a battle change. Speed boosts take effect immediately, so now, you have a +3 speed Coalossal and a +2 SpAtk Coalossal, which kills everything. It is usually used with a Urshifu-R which uses aqua jet, because of coalossal's astronomical defense, and weavile, because weavile has horrible special attack.
So, these are some basics, and these links are excellent resources:
Hope this helps :)
Editor edit: added paragraphs