well you need to apply to a guild to be able to join you can apply here in forum
To join a specific guild find that guild page here and apply https://pokemonrevolution.net/forum/forum/7-guilds/
or make a thread here requesting to join any guild(state the server you play in) https://pokemonrevolution.net/forum/forum/8-looking-for-a-guild/ so any guild that want to invite you invites you