depends on who you ask, but the fact remains: you need to align the back of your hand (the "top" of you hand, I guess) needs to be aligned with the forearm.
Now, the thing I'm talking about, when I say it depends, is on which angle you woudl hit with - the top two knuckles ot the bottom three? I don't know that much about Karate, so excuse me if I'm generalizing, but most karate styles, I think, teach to hit with the top two knuckles. Some kung fu styles, however, teach to hit with the bottom three (middle knuckle - pinky knuckle). Make a fist and look at it from the top - the middle knuckle protrudes so you'r going to have to decide on one or the other.
Karate styles argue that because of the minimized surface area, the impact is going to be harder (there's a lot more other things going into the technique, but that's the main point for beginner).
whereas,
The styles that teach the three knuckles argue that it's a much more natural position, so there's a lot more wrist support, hence more power can be delivered + it's a lot more stable.
But then again, this is only a stranger online posting this, so find someone that knows what they're talking about and ask them in person.
(BTW, I'm saying that you do, but don't say that you "take boxing" or "box" if you aren't training under someone that knows what they're doing - books or videos do not count)