Pokémon Showdown Beginner's Resources

Originally written by verbatim and updated by Scene.
StrategyDex
A comprehensive list of every Pokémon. Clicking on a Pokémon will give you information about it as well as tips and tricks for using it successfully.
Tier Rulesets and Banlists
Up to date information on the clauses and rulesets for each individual official tier, including a list of Pokémon in that tier. For a detailed explanation about the tiering system, click here.
Usage Statistics
Statistics illustrating the usage of Pokémon, their movesets and other characteristics for every ladder available on Pokémon Showdown, sorted by month. This post answers a few of the commonly asked questions about the usage stats.
Damage Calculator
Allows you to calculate how much damage Pokémon will do to one another. You can also find this link by typing /calc into the chatbox on Pokemon Showdown.
Smogon Abbreviation Guide
A detailed explanation of the hundreds of acronyms scattered across the competitive battling scene.
SweeperCalc
SweeperCalc is an advanced damage calculator best used to view how your entire team matches up against your opponent's. To use, simply import your own team and input your opponent's Pokémon into the respective teams. From there, you can either select a set based on usage or input your own data for your opponent's team's specific Pokémon.
bReakMyTeam
Another SweeperCalc tool, bReakMyTeam allows you to easily view how weak your team is to common Pokémon both offensively and defensively.