The Pokémon Rankings is a page where you can check out the highest level Pokémon and stuff. The pokemon Ranking sections primary function is to rank all Pokémon form any type you want or some players use it as a training module, It's used like this if you have a level 20 Houndoom or such you would battle a higher level pokemon so you search for one.
Stuff it includes:
Main Page — It's not really an option there but if you click on the link to Pokémon Rankings you'll be there. Here it shows you the top 35 Pokémon.
Search Via Pokémon Name — You can pick out of any of the Pokémon then click "Search" to find out the top 35 Pokémon of that species.
Search Via Type — You can choose any type of Pokémon and click "Search" to find the top 35 Pokémon of that type.
Search Via Level — You can choose any level then 35 random Pokémon of any type/species will appear. You can "Search Via Level" with "Search Via Type" or "Search Via Pokémon" too.
Search Via Order — Lets you choose how you want the list of Pokémon like.
Current Strongest Pokémon: Blim's ShinyToxicroak Level~768,601