If you mean there chats with other people you need to have acess to their account and can only view recent chats with conversations they have left open.
but if you mean conversations you have had with your own friends then you need to open a conversation with them when there online and hope that the chat is still logged.
You can't unless you are chatting with them. That is the only conversations you will see, the ones between you and them.
No only your firends can see them. If you are talking about people of Facebook which you are no friends with then no. Your friends that do not have facebook can not see your profile or posts.
You can see your friends' posts on Facebook if they accept your requests to be their friends.
no
ES
Yes they do
The original purpose of facebook is to communicate our friends and to see the information of of your friends
See what? Be specific
That depends on the privacy settings used.
it currently does not exist
Yes.
There is currently no way that you can use to put a pass code to your messages on Facebook such no one is able to see them when gains access to your account.