1. Information and understanding about a subject, which someone has in their mind. English = knowledge.
As a Verb or Adjective
1. To have correct information and understanding about a subject in your mind. English = know, (be) knowledgeable.
1. Used alone in response to your addressee's comments or to interrupt your addressee to confirm understanding or to encourage them to continue. English = 'I know', 'Yeah!', 'Ugh huh', 'Hmmm' and so on.
1. Used at the beginning of a sentence to introduce a new topic of conversation.