There is no single meaning, but is used to convey a casual sense of affirmation, acknowledgement, said in agreement, something that is real, absolute, well said, a person dropping mad knowledge while unconsciously projecting who they are onto others and exposing him or her self as a hypocrite.

Or to indicate that something has impressed you favorably but everyone really knows the person doing the preaching is clueless and talking out of their ass.

Its usage among young blacks has been parodied ad nauseam among clueless suburban whites who actually do have a clue and calling out their counterpart who are the ones who actually have no clue.

It means sure, which is used widly used by Snoop Doggie Dog.

It means - well said.

good look or a statement that agrees with what was previously said

Social media driven 'wank-speak' for when another cretin that is like you says something you agree with.

Preach;

to have somebody speak up about a subject with an opinion that is very common and isn’t afraid to repeat it (they’re a preach)

Saying amen and praising an action you have done. Or hyping someone up.