what is the use of snap swivels?
where on the line do you put them?
do you attach them before the float or after the float or do you attach the hook to them?
so l attach the hook to the swivel then?

They were first made for quick changing of spinners. But l use them mostly for cat fishing tie them to the line where you want a hook and snap on a snell, that way when you go home you can easily take off the hooks and still have you're pole rigged for next time(and not risk hooking your interior or in my case kids).

you can use snap swivels for putting your hook on it or putting your lures on so that you do not have to keep cutting your line and you would put it on after you put your float on

the swivel part performs the same function as a standard swivel - it allows free rotation of whatever u have tied on - helps keep line from kinking
the snap part simply makes attaching something at that point easier
when l was a kid we typically used on end of line to attach artificial lure
eventually started using anytime needed to make quick changes - pre-baited treble hook on leader for catfish or sometimes when l was using a multi-hook setup
do not think l ever attached hook directly to snap-swivel - seemed too obvious that fish would see
generally did not use with live bait unless l was usung leaders & drop hooks

l use them to make it easier to change lures, as well as a way to attach bank sinkers to certain rigs so that they can slide along the line on the swivel and not offer resistance to the fish during a strike.

Tie the snap swivel to the end of ur line. You attach the hook to the snap. The snap swivel is more like a combo. The swivel is attached to the top of the snap, the hook gets attached to the bottom of the snap (the part u open & close) They r used to make changing lures quick & easy. The purpose of a swivel is to..swivel!, that prevents the line from getting twists as the lure rotates for whatever reason. Here is a snap swivel, just picture putting a hook on the snap.
http://cabelas.com/cabelas/en/templates/product/standard-item.jsp?id=0000031113969a&navCount=2&podId=0000031&parentId=cat20293&masterpathid=&navAction=push&cmCat=MainCatcat20166-cat20293&catalogCode=IJ&rid=&parentType=index&indexId=cat20293&hasJS=true

snelled hook or lure only...also snaps stop your line from twisting when you're using various lures.

you tie the swivel on (make sure its the smaller end) first like a normal hook to the end of your line and then what you do is you get some hooks with loops already tied on the end or you can do that yourself either/or but you unsnap the swivel,put the loop on and snap it back also good for spinners and other lures