I just went through all of this yesterday so I actually know the answer to this one.

I looked it up on
www.ovulation-calendar.com it's under tools. Anyway, this will help you sort out making the calendar at least. It's not too hard to figure out and I did my own on the PC. Most girls here are using a really advanced chart... I'm not ready yet. It looks too hard and I'm a bit intimidated by it.
www.fertilityfriend.com I also did alot of digging to find the most fertil days, as my cycle tends to fluctuate (shorten or lengthen) about every three months or so. Interestly enough I found a few different aswers to this question. The ovulation site listed above gives a formula telling you to take your shortest cycle in the past seven months and subtract 18 from the total number of days. ie: 28-18=10 then you take that ten count 10 days out from the first day of your cycle. This should be your "O" day. Then I read in one of my planning books that it's usally in the middle of the cycle. So just divide in half.
Then you read some of the posts here and you'll see that everyone is different. I've decided to buy a kit and a therm. Cause my AF seems to change her mind on a whim too. I'm covering all the bases.
Hope this helps.
See ya around!