You have to go to Wally's parent next door and get HM 03(Surf).
You have to beat flannery
Beat the gym leader
Beat the fuchsia city gym leader.
After you have beat wake in pastoria city you have to fly to hearthome city and you can battle the 5th gym leader and get your 5th badge.
You go to Saffron City, go to the Silph Co., take out Giovanni, then beat Sabrina
you get all the gym badges and battle the elite four on an island you get to after you get the fourth gym badge
Beat team Magma/Aqua (depending on the game) at wherever they are at this point, and then capture the legendary Pokemon of the game. Then the doors will open.
latias
Yes.
To get the fifth badge in Pokémon FireRed and LeafGreen version you have to beat Koga. He uses poison type Pokémon.
you have to beat other gym leaders before you can get your hearthome city badge, lol. it's probably the hardest badge to get.
Surf to the right and get the Badge from Mossdeep City.