you don't. you use it in Pokemon sapphire to make your secret base.
At slateport city there's a outdoor market you can buy various items here including the TM Secret Power.
at the top of lake rage when its raining
Secret power is a TM you can buy in the celadon dept store.
the power plant on route 9 i think
Aura Beam is in Pokemon HeartGold.
That is impossible in Pokemon HeartGold and SoulSilver.
No, you cannot sell eggs in Pokemon HeartGold.
you must defeat red and he will give it to you
Some Pokemon learn ancient power as they level up.
in the power plant
He is outside the power plant
hidden power
You don't
there is absolutely no secret apricorn in heart gold or soul silver, but good question.
You can't.You have to surf.
You have to answer anyone you want. He doesnt give you anything.
You can't, unless you mean secret base. You have to have a Pokemon with Secret Power. Use Secret Power in front of a tree or an indention in rock.
Walk around the power plant for a bit
There is no best Pokemon on Pokemon HeartGold.