what are private keys (essentially) how can i make them using any given data? private keys decode pub keys so how can they reveal other things?
can i reveal a web address from a private key?

I should be able to unpack anything from a private key seen as I can unpack something that can read/wrire decoide/encode

right?!
Bitcoin private keys (secp256k1) are just a random 256bits "number" (256 random zero and ones), or say 32byte random data. The only constraints are, that the random number must be between 0x1 and 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD.

You can calculate the public key from your private key but not vice versa (it's not practical possible).

With "revealing a webaddress" you probably mean encryption. You can use Bitcoin private keys with available schemes (Ex. diffie hellman) to derive a symmetric encryption key (ex. AES256) and encrypt data for a particular receiver.