Firstly there's no app for the PokemonDb so I presume you mean the site in general. Next, we have a Pokemon Showdown! server but the software used is not affiliated to the PokemonDb in anyway. However you can create your own servers and name them which is the case for the DB server which can be found here.
At the DB you server you can create teams for each tier and then battle in that tier. If you need more info on the server check out the thread about it here.
If you have any other questions feel free to ask me and I'll try my best to answer them.