Go to Saffron City by giving the guard the tea you obtained from the old lady in the mansion. Then go into Silph Co.
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you go to the 4th gym leader. her name is erika. her strongest Pokemon is a level 29 viloplume.
TM24 is given by Lt Surge after his defeat at the Vermilion City gym.
you can get it if you defeat the fighting gym leader in saffron city but you can only get 1
The third gym leader is Lt. Surge, an electric Pokemon trainer. In the yellow version his only Pokemon is Raichu. Raichu can be easily defeated by a ground type Pokemon. Conveniently, Diglett's Cave is located right next to the town. In here you can find wild Diglett's and maybe wild Dugtrio's, the evolved form of Diglett. These Pokemon can easily defeat Lt. Surge with the Dig attack.
Head back to Viridian City and challenge the gym there (it will be open now) to get your 8th badge. After that come the Pokemon league.