Team building:
What i do is i look at smogon, go to OU (overused) bracket, sometimes UU (underused) and pick the pokemon who fits my playstyle (like Huge power azumarill along with a bulky trapper ferrowthorn) and i use 4 oths that fit into that. First, i would go to Pokemon showdown (website to test ur teams, etc), while looking at smogon for the builds and pick the pokemon i want on my team, while using the smogon build. (Like a huge power azumarill, i would want to put the ability, moves (for azumarill its aqua jet, superpower, a fairy move, and belly drum) and EVs (effort values) and IVs (individual values 5-6 depending on pokemon is good) and nature (in this case its adamant for azumarill) for azumarill. Then i would look at what pokemon fits along with azumarill, mainly a bulky trapper like ferrothorn or Rotom-W and maybe something like Lando-T. The best pokemon for doubles (THIS IS THE MOST OVERPOWERED SPEC IVE EVER SEEN) well not the best but somewhere from the best, i can PM you the builds for the Pokemon. I will do other posts later.
Before you teambuild, you need to decide what metagame you wanna play in. I reccomend using pokemon showdown to start. If you're not interested in smogon, then I can't help you. Anyway there are different tiers, they are not based on how strong a pokemon is but on how high their usage is. Of course stronger pokes make it into higher tiers.Every three months there are tier shifts. Some pokemon that are used a lot in a higher tier can move up a tier, and the same goes with lesser used pokemon dropping to a lower tier. This is all based on usage stats, which is data colected by Pokemon Showdown of what pokemon are used the most and their most common movesets. If their usage is 3.7565% (or a pokemon that you will encounter at least once every twenty battles on the ladder) they will be moved up, if they drop below that number they will be moved down. There is also BL (borderline) which means they are too broken to be used in the tier below them, but not relevant enough to be in the tier above them. For example Mega Houndoom is too broken and unfair to be in RU and therefore banned, but it's not good in UU either so it isn't really used much and not relevant enough to be considered UU. You can still use lower tier pokemon in higher tiers, but you can't use higher tier pokemon in lower tiers.
When you're buildng a team you need to have different roles, and synergy. Synergy means having different types to cover eachothers weaknesses. But it's not as simple as that. Just because you have Gengar that resists fighting, and say a Chansey which is weak to fighting, you're still destroyed by Conkeldurr. Conk can easily live a hit from Gengar if it's Assault Vest, and use knock off, a dark type move and kill it, as well as drain punch on Chansey. My point is that you have to make sure your team can handle certain threats because most pokemon carry coverage moves.
Ubers OU UU RU NU Little Cup (Unevolved Pokemon) Example of usage stats- I could only find the ones from October but they should have ones from June.
These are the rankings that show what pokemon are good in a certain tier, some pokemon are still very high ranked and useful even if they're from a lower tier.
As for EV's basically everytime you defeat a pokemon you gain evs, for example if you kill an Allakazam you get +3 special attack evs, and if you defeat a Blissey you get +2 HP evs and +1 Sp. Def EVs. You use these to your advantage and train a pokemon to its potential. You can have 508 EVs per pokemon. Like if you wanted to train a Weavile in attack and speed you would defeat Zubats and Trapinches since they're easy to find and defeat, and because Trapinch gives you +1 attack EV and Zubat gives you +1 speed EV.
IVs you have to breed pokemon for and I'd just buy pokemon off someone on the forum because its hard to explain and a pain in the ass to breed, but basically every Pokemon has different IVs and some pokemon are just better in certain areas. But you can breed so that they're perfect in all areas.
You also want natures to be used to your advantage. Like if you're breeding a Mienshao you want it to have a Jolly nature to raise speed and lower special attack since Mienshao isn't a special attacker and needs all the speed it can get to outspeed other mons and possibly win a speed tie with another Mienshao. Basically all natures lower one stat by 10% and raise another by 10%.
Also I don't mean to brag but I was in the top 40 ranked UU players last fall. But I haven't played much since after ORAS
I honestly learned from just throwing a team together based on what I read up on Smogon and learned through lots of Showndown battles. Read up on Smogon is my best advice, if you want more pointers feel free to PM me. If you got no idea where to start, try random battles on Showdown to get a feel for predicting your opponent's moves.
