Pearl clasps are traditionally used to finish the ends of pearl necklaces. They're wonderful for necklaces that includes expensive materials because the box-style clasp has a catch inside making it extra secure.
Barrel clasps are best for necklaces (not bracelets). The screw action is easier for some people to open and close than the triggers on spring rings and lobster claws. Most barrel clasps tighten and loosen with screw action, but a spring loaded barrel clasp works by twisting a peg into a notch. To use these clasps, attach the outside loops to the ends of your stringing or beadwork with jump rings or crimps.
Fold-over clasps operate on a hinge, similar to the closures on some wrist watches. These clasps work great for making bracelets and watches because they can be opened and closed with one hand. On vintage "assembly" bracelets (now called treasure bracelets), you'll often find a rhinestone bauble soft soldered or glued to the plated fold-over clasp. Fold-over clasps are still popular on the disk-and-loop bracelets used today, but instead of rhinestone assemblages, we normally see artisan-created polymer clay, dichroic cabs, or cool ceramic pieces glued to the disk bracelets.
Snap Clasp findings (also known as "ball and socket" and "button clasps") are nice clasps for people who have a tough time with lobster clasps and spring rings. You "pop" them open and closed like a snap. Get them while you can - these may be permanently unavailable soon.
What's the difference between "white" and silver plate? Silver plate has a thin layer of actual silver, so it's a better match for sterling silver jewelry. However, like sterling silver, silver plate can tarnish rapidly. White plate, while slightly grayer, does not discolor easily.