Okay. So first you need to beat Roxanne. Once you've done that you help the Devon guy. After you get the pokenav you go to Mr. Briney's(i think that's his name). he will give you a ride to Dewford. that is where the gym is.
The second gym is the Dewford Town Gym with Gym Leader Brawly.
Dewford town.
Find cut
go to slateport then to the aquaraim
Pokemon ruby where is the 6 gym
Norman's gym
its the petalburg gym and/or gym 5.
petalburg gym
The 6th Gym Leader In Pokemon Ruby Destiny is in Down Pour City
In the 8th gym. he is the gym leader
Wattson the electric gym.
In fire red/leaf green it is in Cerulean City in sapphire/ruby/emrald it is in Mauville City