Jailbreak redsn0w can't let me download in Cydia?

I installed Cydia using redsnow and when I was done, there's a cydia app in the menu. So I tapped it and pressed featured which is because I wanna download themes. So I tried to click one but it says "Can't find package" and it says I should download more sources. How do I download these sources? Or at least how do I get around to this obstacle? I had an iphone 3gs with ios 6.1.3 before jailbreaking if that's anywhere useful.

Because you just jailbroke you don't have any sources. To add a source you go to "manage" on the bottom of the screen, then press "sources" then press "edit" at the top of the screen then press "add" and enter the source. If you don't know any sources try searching the theme you wanted on youtube and it will most likely give you a source to go with it.

Hope I helped.

Simply download winterboard to install themes
Also add these sources and have fun with those
http://iphone.pandaapp.com/news/05222013/the_best_cydia_sources_and_repositories_in_.shtml