What do each of the 3 numbers represent?

If the ratio is listed as 6.3:1, that means that with one complete turn of the reel handle, the spool turns 6.3 times

And if it is a 7.0:1 that can also be read as 7:1 meaning that there will be 7.0 or 7 (which is the same thing) turns of the spool per 1 turn on the reel handle.

Generally, higher gear rations are best for soft plastics and lower gear ratios are used best for lures with trebles. This doesn't necessarily mean that if you want to throw a crank bait you will have to do so on a lower gear ratio reel like a 4.6:1 or a 5.1:1 (those are just example ratios). Or if you want to throw a Texas Rig you will have to do so on a 7.3:1. You can experiment around throwing different types of lures on different speeds and see what you feel is best for you. I personally just bought myself a 5.1:1 reel to use specifically for throwing deep diving crank baits. However, Keith Combs, a professional bass angler likes to use high speed reels for this. It all comes down to personal preference.

To me gear ratios are marketing points. What I really want to know is IPT. Inches per turn. How many inches of line the reel will retrieve per turn. A small diameter spool at a high gear ratio will retrieve less than a larger diameter reel with a lower gear ratio.

This is spelled out in the Lews specs. They show ratio and IPT

IPT doesn't mean a thing when the reel is not filled full.

So,as you cast out,say 50 yards of line, the reel speed(IPT) increases as you retrieve?

a larger tire turns more inches per turn than a smaller tire