Well I don't use a Mac so I can't give you specifics there, but I have opinions that should branch across operating systems.
Some people will sketch their stuff on paper, ink it, then scan it into their computer. I don't know all the technical details on this, so maybe one of those people can drop by. But do know that it IS an option to work completely traditionally and then put it online. That may be the way you want to go if you aren't looking for a lot of special effects.
I do most of my work digitally, so that's what I'll share.
For drawing software, I recommend Manga Studio
. It's drawing software that's comic-oriented. There's the regular version and an Ex version, but the trial is for the regular version. You may not need all the bells and whistles the Ex version has if you're just starting with digital art, anyway. You can always upgrade the basic to Ex later if you change your mind, so it's pretty much better to start with the basic version.
There is also free software available, but I don't have any off the top of my head that are Mac compatible. I'd thought GIMP was, but I can't find a Mac download for it right now. Sorry.
Most of us who do this regularly (and digitally) use tablet pens. Wacom
is pretty much the go-to business for drawing pens. If you've never used one, what you'll probably want is the Intuos Pen or Intuos Pen & Touch. (These two models are basically the same, except the Touch version also works somewhat like a touch pad.) These are the cheaper ones (around $70-$100), but cheap doesn't mean they don't work well.
As far as tablet pens go: some people have trouble getting used to the disconnect of looking at the screen while they draw (as opposed to looking at their pencil tip). I've heard people have an easier time getting used to it if they buy either a medium or large sized model, since the trick is learning to not use your wrist so much to pivot. I don't really have an opinion, since I've had the same tablet for 10-ish years and it's a small sized one. But that would be something to ask others about, or google.
Some people use their mouse, but a big reason against it is tablet pens give you pressure sensitivity. So the pressure you put into it affects the line weight (like it would with a pencil or with real ink). If you have Illustrator and know how to use it, you could make comics with simple vectors
. This may be the easier way to go if you'd rather use a mouse, but may not be best if you don't already have Illustrator (in terms of a price tag) or another vector program.
Definitely no one way to do things, so it's usually a matter of deciding what you're most comfortable with and exploring those options. Hope that helps a little.