You have to have at least ten Pokemon. then go to the first cave you need to use it in. come out the end you originally enter and exit. now go to the building to the right of the Pokemon center. go to the top floor and talk to the man in the labcoat. he is proffeser oaks assistant and he will give it to you.
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!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Most electric type Pokemon can learn flash.
flash will work on buttefree and zapdos
At flashy flash flash city