Go through Diglett's cave up to Pewter city and go down to route 2 you cut down osme bushes with cut and there is a big building and you talk to proffeser oak's aid inside and if you have more than 10 different types of Pokemon he gives you flash
how do you use flash? just go to pokemon and go to the pokemon that knows flash. press A and it will say in blue text "Flash" select that and it will use Flash. it's very useful in dark caves.
The place where it flashes is where you can find the Pokemon It would flash blue if it was found in the water
Look at "How do you get hm flash in blue?" On this site.
Voltorb is the best choice cause he isn't useful
flash works on abra, voltorb, clefairy, jiggly puff, and MAYBE charmander, but mew, mewtwo, and some other normal or psychic types.
any fire Pokemon and some leaf Pokemon but you shoulb be able to find a Pokemon near the cave youre going in
Go east(or right) of cerulean city(you'll need flash to get through the cave)
In Pokemon Platinum, Flash is a TM.
Flash!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
flash will work on buttefree and zapdos
Most electric type Pokemon can learn flash.
At flashy flash flash city