1. Go here and go to ''Play online''.
2. Then make ''Teambuilder'' for starting make teams.
3. After that, you can battle, this is online, don't need wifi or nothing!
4. Go to ''Choose Name'' and make your name!
5. Go to the Icon where you can see in the top at right, click there and make Register, make a password and done.
6. Have fun!
Also this is the Pokemondb's Pokémon Showdown server! You can battle friends more easy there because it only have 10 people..
Hope this helps!