There's A LOT of traffic going through Cydia right now, so a lot of things might take multiple tries to download. If you can, wait a few days until you try again. There has been over 4 MILLION DOWNLOADS in the past 24 hours for the new jailbreak!
All you ready do is search for stuff in Cydia. You can add things called REPOS....which can give you a better selection of apps and tweaks. I can explain that down below
Winterboard is a great thing to have, as it lets you download a lot of themes for your phone.
And, as you've found, there are a lot of good emulators. I use my Genesis one a LOT to play Sonic <3
(you need an account to see links) is a good REPO to add. Go to this website on your computer browser, and it shows you how to add different REPOs. A lot better then I could explain lol.
(you need an account to see links) has a list of more great ones to add, and the apps to watch out for.
Tweaks help customize the user interface of your iphone.
(you need an account to see links) Has a video showing a lot of great tweaks for your phone. A lot of these cost money (unless you add the xsellize repo -cough-).
If you have any more questions, PM me hun C:
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(you need an account to see links)