owner: main key that controls everything and can change all keys including owner key.
active: "coin" transactions such as spending Steem, powering up, etc. Can't change the owner key.
posting: social actions -- posting and voting. Can't spend coins or change keys.
memo: used to encrypt and decrypt private messages
Thank you. Is the owner key also used for mining?
I don't know which keys are needed to mine in an existing account, although it probably includes the signing key which isn't listed there but is yet another key that is part of the witness data attached to an account. When you mine without having already created an account you just give one WIF key and it is inserted in all the slots when the account is created.
What and where is the WIF key ????