After jailbreaking my iphone what now?

I just bought a 3G iphone yesterday. SO, I heard that jailbreaking iphone is good cuz you can put in third party apps etc.. So I tried it using quickpwn 2.1. I installed ‘cydia’ and ‘installer’ not even sure what they are for, but I didnt change the boot screen. Now I have these two additional icons sitting on my iphone menu, what exactly do they do??? Where do I go from here??
How can I add third party apps?? Preferable through my laptop cuz I’m not too keen on using wifi on my iphone at home when I have a cable connection available!
Then comes iphone hack toolkit 1.0 (recommended by the iphone theme website I visited) I imported some pkg files (are they only for themes???), applied the themes, but HOW can i change back to the original theme?? There seems be be no such option in the iphone hack toolkit…
So can someone here help me out???
Answer all my questions… Thanx!!!
Answer #1
just go to cydia and download apps there