Hey there! Nice to see you here.
I think you can start charting right away, however since you're just coming off of a birth control method and you're wanting to chart to TTA (try to avoid), I would advise that until you have clear charts, charting should not be your ONLY form of birth control (i.e. use condoms or a diaphragm all the time be cautious that you could be fertile at any time). Once you start noticing clear charts, then you can loosen up the use of contraceptives.
There are two main charting programs that people seem to use (I have tried both):
FertilityFriend: Great charting site, nice and simple. They have a free version (Basic Account) and a pay-to-use version (VIP Account). The Basic Account is about that... basic. It's good and it'll get the job done (you're able to temp, mark your CM and CP, HPT and OPK tests, and when you BD), but the VIP Account has a lot more options, which can be very helpful. They're VIP Account is subscription-based. You can pay for a 30-day ($10), 90-day ($25), or 365-day ($45) account. You get to have your own webpage where others can view your charts. Here's my FF chart page:
http://www.fertilityfriend.com/home/niamhdhabolt
Ovusoft Software: This is a software program that you install on your computer. You can get a 15 day trial from their site, or you can get the "Taking Charge of Your Fertility" book by Toni Weschler (whether you use this software or not, I *
highly* recommend this book!!!) and the book comes with the CD and a 15-day free trial. The full version is $40, but you have it forever. It's not subscription-based like FertilityFriend, so you won't have to keep repaying for the extra options. With Ovusoft, you also get a webpage like FF, though it's set up differently. Here's my ovusoft chart page:
http://forums.ovusoft.com/chart.asp?id=niamh_dhabolt
I *personally* prefer Ovusoft, but most people seem to use FF. I definitely think it's worth the amount.

Right now I have the VIP FF and Ovusoft at the same time (I bought the VIP FF before I found the Ovusoft program), and since I like Ovusoft better, I'm using that one as my main charting program. I'm using FF as back up, and when the VIP status runs out, I'm just going to use their free version as backup to my Ovusoft program. lol.
With the personal websites... some of the pros and cons (IMO) between FF and Ovusoft:
On FF, you can add pictures on the top. On Ovusoft, you can't.
On Ovusoft, you can change the colours of your charts. You can't on FF.
All your charts are listed on one page on FF, on Ovusoft only one chart is shown at a time, but there's an option to view previous charts.
There are other lesser-known and lesser-used programs out there and I've checked out a few of them, but I'd definitely consider FF and Ovusoft to be the best.
Anyways, I got to go to bed, so hopefully this was helpful.