i have a whole lots of good questions i think i need people who are intelligent bible scholars who can provide answers to some questions ?

i have questions about the following bible verses and i hope someone will be able to shed more lights on those
Genesis 4
Cained killed Abel and God had him sent away to a land and he had a sign on his head so he wont be killed
my question is who are the people God wants not to kill Cain where are they from ?
biblically we know there was only Adam and Eve ?
Genesis 4:17 Cain knew his wife
who created the wife ?