if i cracked my macbook screen while i have apple warranty will i be able to get if fixed for free?

No, not under the 1 year warranty. If you have AppleCare + there is accidental damage coverage.

It's just like owning an automobile, you buy a Ford and wreck it, you file a claim with your insurance company, not Ford Motor Company. Manufacturer's warranties cover defects in material and workmanship.

It's not free, though, there's an excess, isn't there (or is that just standard AppleCare)?

If you mean the covered user has to pay a fee you're correct. It's sort of a deductible payment sort of thing.

The 12" MacBook was discontinued over 2 years ago, so it's impossible that it would be under warranty.