I've heard from a friend taht if you train and give an eevy a certain stone..

It has a grain of truth, but it does not hold for Leaf Green or Fire Red and they must eveolve with friendship. Eevee evolves into Espeon between the hours of 0000 and 1159 or Umbreon between 1200 and 2359.

I hate to tell you this, but your friend has brain damage! (Kidding, he's just not as well informed as I am! Tell him he needs to hang around SC more!) He's got the idea, but the details are all wrong!
OK, you can make your Eevee become one of 5 evolutions, but only 3 in FR/LG. You can get Jolteon by giving it a Thunderstone, Flareon by giving it a Firestone, or Vaporeon by giving it a Waterstone. You can do this at any time that you want, any level, etc., but that's all in FR/LG.
Now, about the color changing stuff your friend has misinformed you about-he's refering to Espeon (pink) who's a Psychic-type and Umbreon (black) who's a Dark-type. You CANNOT get them in FR/LG because there is no "time" in those games. You CAN do it in R/S or Emerald, but it's backwards in Emerald...In Ruby or Sappire you'll need to do a Friendship evolution-no stones needed (it has to love you to get these evolutions!! Check with the lady in Verdanturf to see if Eevee is really happy with you-it should say something like "it couldn't love you anymore" when it's ready.) and if you raise it one level during the game hours (look at the clock in your room) of 6PM-6PM (night time)you'll get an Espeon, if it's between 6AM-6PM (day time) you'll get an Umbreon. The times are reversed in Emerald, so do the opposite if you're in there. Or, you can get them both out of Pokemon Colosseum for GameCube as they are your starters in that game! (The game should be around $15 used/$20 new and the cable is like $2 to connect your GC to your GBA. A used copy of R/S will run you maybe $20-$25, Emerald is still more expensive, but the holidays are coming up...)
Please inform your friend of the actual story on these evolutions, OK. Hope this cleared things up for you!

Eevee is the evolution Pokemon do this certein stuff to get him

Flareon - use a fire stone

Vaporeon - use a water stone

Jolteon - use a thunderstone

Espeon - make it like you and level it up in the day

Umbreon - make it like you and level it up on the night.

Theres two more evolution that eevee has but it's only available in the new for ds called Pokemon Diamond/Pearl

I know this a bad thing because I double post, but I forgot to tell you that in order to get Espeon and Umbreon, you need to trade it to Emerald/Ruby or Sapphire.

No that is not true, if you train a Eevee in the day it will evolve into a Espeon and if you train it at night, it will evolve into a Umberon.

you can give it a sun stone 2 b flareon or a water stone 2 b vaporeon or thunder stone 2 b i forgot its name now or u can give a moon or phsycic stone