Differences:
VGC is a format that uses a ruleset. From Gen 6 onwards, there's been a pattern: Rrgional Dex, National Dex and Restricted Legendary (where you're allowed two restricted legendary Pokemon).
Doubles OU is a tiered metagame where you bring six Pokemon instead of VGC's four. Pokemon like Zeroara, who is banned in VGC since it's a mythical, and Zygarde, who is banned in VGC 2021 because it's not a restricted legendary format.
2 v 2 doubles, as the name suggests, is where you take two Pokemon in DOU.
VGC Teambuilding:
Always consider the meta. Currently, Urshifu is the highest used (check on Pikalytics for more usage stat information) so you'll want a check to it, like Tapu Fini. Mame surse to have supporters on your team, with moves like Tailwind, Fake Out, Helping Hand, Trick Room, etc. Tailwind and Trick Room are speed control, which is very important in this format. Every team should have speed control, but it doesn't always have to be supportive. Dynamaxing Thundurus-I can raise speed with Max Airstream, meaning it can be a team's speed control whilst dealing high damage. Dusclops is a great Trick Room setter and pairs well with Metagross and Glastrier, as their low speed tiers mean they function well in Trick Room, and Dusclops has ways to self activate their Weakness Policys with Bulldoze and Rock Tomb. Whimsicott and Tornadus-I set Tailwind well, both of them also having a great support move in Taunt, blocking Trick Room and set ups. Incineroar is amazing in VGC because of it's combination of Fake Out, Intimidate and Parting Shot. Intimidate is incredibly useful in VGC, lowering the ttack of both opponents, weakening their damage output. Follow Me and Rage Powder support is also very useful. Amoonguss and Clefairy are the main users of it in this format, since Togekiss has been highly debuffed by the amount of threats to it that have been introduced. Amoonguss is also used for its Spore, sending the opponent to sleep with 100% accuracy. Clefairy has Helping Hand to help an ally by increasing the damage output. The main offensive Pokemon in this format I'll go through now. Urshifu-Single Strike is the most used Pokemon in this format for a reason: it's huge damage output. It counters Glastrier and Metagross with it's STABs and has priority in Sucker Punch. It does a lot of damage when hitting neutrally, too. Tapu Fini is a huge special attacker, tanking special hits and hitting very hard after a Calm Mind. With Muddy Water, it can hit both opponents and Moonblast is it's fairy STAB. Regieleki is very good when used as a dynamaxer paired with Inteleon with a Chouce Scarf to use Soak to make Regieleki hit everything super effectively. Thundurus-I is a great dynamax threat, supporting Urshifu with it's dynamax moves, Max Knuckle, Max Airstream and Max Lightning hits Urshifu's main threat Tapu Fini. As I menftioned earlier, Glastrier is amazing paired with Dusclops. Other attackers include Zapdos, Kartana, Landorus-T, Coalossal, Rillaboom and Galarian Moltres.
Hope I helped!
