If I generate a sha256 digest from some text I get one string of letters and numbers, but if I generate a key pair using bitaddress, using the same text I get a private key.
What is the relationship between the digest and the private key?

Also I thought (and I'm probably wrong) that putting some text through the Sha256 algorithm produced a 256 character string of ones and zeroes.  If that correct. If so how do we them get the digest?

Thanks for your help in understanding this