If you block someone, they will not be able to find you in a Facebook search, see your profile, or interact with you through Facebook channels (such as Wall posts, Poke, etc.). Any Facebook ties you currently have with a person you block will be broken (for example, friendship connections, Relationship Status, etc.). Note that blocking someone may not prevent all communications and interactions in third-party applications, and does not extend to elsewhere on the internet.
(this is straight from facbook.com under the privacy settings)
Chat with our AI personalities
Yes. You can't do anything with them. Nothing.
You can't. Not until they unblock you.
Go on ACCOUNT...... then PRIVACY SETTINGS..... then click on BLOCK LIST and the list of people you blocked will appear then you can choose to UNBLOCK any of the people you have already blocked
you cant
They actually can, but it appears from a person with no link (i.e. name is in black) and no photo