I have seen in Cricket matches that the umpire confirms whether the ball made contact with the edge of the bat before hitting the stumps, what is the significance of this. If the ball doesn't make contact with the bat before knocking the stumps off will the decision still be bowled ?
- Out Bowled
(a) The striker is out Bowled if his wicket is put down by a ball delivered by the bowler, not being a No ball, even if it first touches his bat or person.
You are outlining the scenario where the batsman edges the ball before it hits the stump, so the decision would still be that the batsman is bowled out. In the modern game, umpires sometimes spend a few seconds after a bowled decision to verify that the delivery was not a no ball. Perhaps this is the confirmation that the umpire is seeking, which you seem to have confused with something else.
In addition to Law 30, which (as CodeNewbie quotes) states the striker is out bowled "if his wicket is put down by a ball delivered by the bowler", you also need to be aware of Law 28 on what constitutes the wicket being "put down".
For a batsman to be given out bowled, it is not sufficient for the ball to hit the wicket without either a bail being completely removed from the top of the stumps, or a stump being struck out of the ground.
(Link to Law 28: https://www.lords.org/mcc/laws-of-cricket/laws/law-28-the-wicket-is-down/ )
You might think this stipulation is pointless and that a wicket will always be broken in one or both of the above ways if a ball hits it, but in fact that is not always the case, although the exceptions are obviously quite rare. Usually they occur when either the ball just barely brushes the edge of the stump or the ball trickles onto the wicket at very low speed. Whatever the reason, if the bails remain intact and no stump is removed then the batsman is not out. Here is an excellent Youtube video showing six examples:
Incidentally, before the Laws of Cricket were recodified in 2000, they defined "wicket down" solely as the complete removal of either bail from the top of the stumps, without going on to add "or a stump being struck out of the ground" as is the case today. This old codification of the Law occasionally produced even more bizarre cases of the batsman being "not out" - in 1947, for example, playing for New South Wales against Victoria, the Australian test player Arthur Morris was clean bowled middle stump, but because the 116 degree heat had caused the varnish on the bails to glue them to the other stumps, they were not removed and thus Morris was not out. The amendment in the 2000 Code means Morris would not have got away with it as the Laws now stand.
Here is a link to the Morris incident: https://books.google.fr/books?id=KDIxbom3Wb4C&pg=PT131&lpg=PT131&dq=bowled+"not+out"+bails+heat&source=bl&ots=3tki6LKejF&sig=uO00zQ_lv0-EmtIPJseRB6EKkR4&hl=en&sa=X&ved=0ahUKEwi-9IH8wN7RAhWCchoKHQLBBdoQ6AEILTAD#v=onepage&q=bowled%20%22not%20out%22%20bails%20heat&f=false
I suspect that you are talking about the Ultra Edge used as part of the DRS.
That is used only in case of LBW or Caught forms of dismissal. In case of LBW, if the ball has hit the bat before hitting the pad, he is not out right away, and they can avoid the ball tracker altogether. In case of Caught, well, it is quite obvious why they want to check for the edge.
Umpires don't check for edges in case of Bowled decisions, because if the wicket is down by a fair delivery, batsman is bowled, regardless of whether it hit the bat or the batsman's body along the way. (By the way, according to Brad Haddin, it is also okay if the wicketkeeper gently helps the ball onto the stumps when the fielding side really needs the wicket. ;-) )