When I put in
AA05F15D112414670BAD47FCCC52AD6486D5CB33BEA4463E8DFF0C5B1C1F4D1501
I get an error:
Cannot Decode! Invalid Base58 Character(s)!
That's because it isn't a base 58 check encoded private key (what you normally think of as a private key). That is the hex of the actual private key, just a really big number.
So is there any tutorial or examples can that show how to decode/encode the base 58 private keys. I am still confused.
You already have decoded the base58 check encoded private key. As I already said, you have the key in its hex format. You can convert that to decimal if you really want to. You have the key in hex so you can check whether it is greater than 0x01 and less than the large hex number I posted earlier.