you have to go into the abandoned hotel above the science lab. make your way through the building (there are some scientists and robbers in there, be careful, their pokemon are pretty powerful. use water/ground against the robbers, and fire pokemon against the scientists) when you get to the end of the building, there should be a key to open the door to cinnabar gym. you also can find a few TM's in there (i think one was ice beam, but i cant recall). when you get inside the gym, you have to battle every trainer there, or else you cant get to blaine. bring one or two good water pokemon, and maybe a good ground pokemon as well. blaine uses an Arcanine, a Magmar, and a Rapidash. make sure your pokemon are lv. 45 or more. this battle isnt hard as long as you can knock down blaines pokemon as fast as possible. when you beat him, you get the 7th badge.

i beat the first 6 gym leaders but i do not know where blane is. i went to cinnaber island but the door is locked

Blaine is on Cinnabar Island but you have to swim from Pallet Town to Cinnabar.