What are those crystals for?

[Kiryu]

So, i started played this game and went to the chao garden. I tried to use the two "crystals" or whatever they are with the chao but nothing happened. What are they for?

[Remie]

They should increase stats of your chao, eventually giving it new abilities (walking, running, swimming, flying).

[Kiryu]

I imagined that, but i can't give them to my chao. Maybe it's not possible at the begining?

[funewchie]

You can give them Chaos Drives (the crystals) right from the get-go.

Of course, you can't hand it over to the Chao if it's asleep (laying on the ground). If it's asleep, it's better to let it get it's rest (awakening it early will likely shorten it's lifespan).

The Drives will increase a stat by a couple of points, but the animals give much better increases.
The advantage of the Chaos Drives, though, is that they won't add any animal parts to the Chao, and they don't subtract from other stats (like most animals do).