The Legend wrote:
so how do they sign players so quickly? is the agent waiting around for example at kvb's house or do they just agree to terms and then figure out the details of the contract later
I think what is bolded is how it goes down most of the time. The coach or whomever is making the offer has a deal with some rough numbers (We'll give you a five year deal worth $40M) and then the player can say 'sure, that sounds like what I'm looking for'. At that point they've come to an agreement, and thereafter it's up to the front office and the players agent to finalize the deal and get the pen on paper.
Remember, when free agency starts there's no action going on at the practice facilities, so they don't have to be under contract to feel safe to practice or anything like that. They just come to an agreement, then once the deal is finalized it has to be submitted to the league office for approval. That's the final rubber stamp on making it valid.