if you fully beat it (all 7 gold symbols) and talk to scott he will give you a starf berry
Beat Elite Four.
lv 100
After you beat the Elite Four, go to the Battle Frontier.
beat the battle frontier!
yes
beat all battle frontier leaders
after you beat a certain amount of challenges you will battle a frontier brain which is sort of like the gym leader. if you beat them you get a symbol
Consecutively beat each facility to do so.
You can access the Battle Frontier and you can catch some legendary pokemon.
There is no Battle Frontier in Ruby. Only in Emerald, Patinum, HeartGold and SoulSilver.
yes when you beat the battle frontier with all gold metals
No it's already unlocked. You can even go in there before going in any other buildings at the battle frontier.