Moreover, consequences aren't what make good will good. If you took five minutes out of your day to walk an old lady across the street, no one could be mad at you if a fucking hipster on a runaway fixed-gear ran her over as soon as you got there; that would not diminish the goodness of your act, since good will motivated it. If you tried to save a box of kittens from being sent into space, but didn't get to them before some asshole hit the 'kitten launch' button, you still did the right thing.
Now, some dickheads think that the highest good is happiness or pleasure or some bullshit like that, and we ought to focus on that. If that's true, then Nature or God or whoever the fuck is in charge fucked up royally in giving us reason, since instinct is more than enough to get us pleasure. Do you really think all of Aristotle's hard work made him happier, in any sense of the word, than the Roman emperors who sat around all day eating and drinking? Darwin? He had depression, for fucksake. He didn't think publishing the theory of evolution would make him happy - but if not happiness, what the fuck is reason for? Answer: to produce that good will you've already heard so much about. We must use our reason to do good.
You might be asking, "Kant, how does reason help us develop a good will?" Well, I'm glad you asked, and if you'll step right over here, you'll see this little thing I like to call duty. We all know what duty is. (Heh.) It takes a strong reason to determine one's duty, and a good will to execute it - these are right actions, actions done because we have a duty to do them. After all, if you help that old lady across the street because she offered you five bucks, what's so great about that? Nothing, that's what. We have to ignore our inclinations, even if our inclinations point us in the right direction. It's only truly a worthy action when you do it because you ought to, because you have a duty to help her, even if you (1) don't particularly give a fuck and (2) now don't have time to watch that episode of Fresh Prince before your meeting tonight. That's character, doing the right thing when you don't want to. We're commanded to love our enemy, but that makes little to no fucking sense - how can we be commanded to love? Really, we are commanded to act with love, with good will, toward our enemy, even if we seethe and boil with rage at the sight of his smug fucking grin.
Only actions done from duty have moral worth. Simple enough. But more than that, they have worth because we will them from duty, never because of some aim we attain or even intend. Do we have a duty to beneficently help old ladies cross streets? You bet your ass, but those actions aren't right because old ladies get helped, they're right because we are correctly motivated. Ultimately, our duty (heh) comes from respect for the law. What law, you might be wondering? British common law? International maritime law? No, idiot - the law must be universal, since it's based in reason and binding on all rational creatures. If birds developed reason tomorrow, they would already know the law I'm talking about. That's how serious this shit is. So we want to always act in a way such that we wish everyone would act that way. And by that I don't mean, we should act for outcomes that everyone would want, since outcomes don't fucking matter, and I don't mean that we should act from desires we think everyone should have, since our desires and inclinations are also irrelevant. I mean that we should be guided by a principle, a maxim, that overrides our desires and the outcomes, such that we want that guiding principle to be a universal guiding principle. This universalization is where our reason comes in, and helps us develop a good will.
Let's say I promised this girl that I would take her out to dinner but my bro has sweet fucking VIP tickets to that thing tonight - should I go? Well, do I want the principle "Keep promises except when convenient" to be universal? Fuck no. Fine, but what if my best friend will fail out of school if I don't help him? "Keep promises except when they have bad consequences" - also bullshit. Sorry bro, but I'm going to be virtuous as fuck tonight, since I really want to help you but have a duty elsewhere.
Look, it's not always easy to abstract away from our inclinations or desires - sure, we have an intuitive notion of right and wrong, but our conflicting desires and expected consequences get in the way. That's why philosophy is so goddamn important - to restore our sense of duty (heh heh) and allow us to make the right choice, whatever may come our way.
Project Gutenberg has a translation of Metaphysic of Morals online; if you prefer paper, you can get any one of several translations from Amazon: Fundamental Principles Of The Metaphysic Of Morals.