I'll help you how I can, which isn't very much possibly. I know Dreamweaver and Photoshop well but never really used Flash.
Basically the way Adobe worked for their programs, you had earlier programs, CS4, CS5 and CS6 (which were actual software programs that weren't part of the cloud), and then they discontinued the CS and Creative Cloud took over. I think it technically came into being sometime while CS6 was out, but any rate, if you're looking for an up to date program, you need to sign up for a Creative Cloud trial. You get a free month's trial and after that they charge a subscription. All of the Adobe programs are now part of the Creative Cloud.
Flash builder is still on there, so it's an option. You don't have to download all the programs btw, but if you choose a 1 month trial of Flash Builder, then it will be from the Creative Cloud.
A lot of people are blocking Flash now, so you might find that the purpose you intend it for isn't as solid as it used to be. I don't know what Actionscript is but the program should tell you what it needs to run.
Also, while personally I'd check out an older version of the program that's off-subscription, you get a lot of fake Adobe and other programs through Amazon. Also I remember hearing that either Adobe or Microsoft won't always honour purchases from Amazon and other sites, so I'd be careful. If you're a student, you'll also find that you'll get big discounts off subscriptions for Adobe. I got my CS5 software back when I was a student and it saved me a lot, but I also found signing up for a Dreamweaver subscription (back when I was using it) through an international site saved me a lot too. As you're in the US I think, you'll probably find Flash Builder subscriptions are cheaper there anyway.
If you're looking to build something for Flash, then Photoshop won't be the right program.