Im curious in what the guards see when they put their machine on your card, do thye see how much money you have on the card of do they see where you last touched in etc

They can see a full history of the cards use - if you press your card on an Underground ticket vending machine you will see a similar report of all your trips. On some Overground ticket machines (not all) you will see an abbreviated report of the more recent trips.

I believe they can also see who the registered user is.