When you create your HIVE account, you are usually given 4 types of keys. Most of the time, however, these are kept secret on the blockchain. If you were given a username/password, then all 4 of these keys are saved on the blockchain and accessible only via that username and password. Here are the types of keys you should be aware of:
Posting key
The posting key allows accounts to post, comment, edit, vote, reblog, and follow or mute other accounts. Most users should be logging into Hive every day with the posting key. You are more likely to have your password or key compromised the more you use it so a limited posting key exists to restrict the damage that a compromised account key would cause.
Active key
The active key is meant for more sensitive tasks such as transferring funds, power up/down transactions, converting Hive Dollars, voting for witnesses, updating profile details and avatar, and placing a market order.
Memo key
Currently, the memo key is not used.
Owner key
The owner key is only meant for use when necessary. It is the most powerful key because it can change any key of an account, including the owner key. Ideally, it is meant to be stored offline and only used to recover a compromised account.
