Many People already know how to do this, but if your new and want to download and install apps from our site or anyother site its actually pretty simple...
First of all you will need some sort of way to connect your iphone/itouch to the
computer eg. Iphonebrowser, ibricker, winscp etc.
If your a windows user then we have a guide that you can use that helps you connect your iphone/itouch to the pc
here
Once you have done that, its pretty simple from here
1. Connect iphone to computer
2.open up the /<root> folder with in your iphone through winscp
3. Then you should see an application folder, just drag and drop the folder with your app, ex: Example.app
4. Next which took me a while to figure out when I was introduced to the iPhoe/iTouch hacking world was setting permissions, you need to set the permission to 0755, dont worry I'll show you how
5 Now double click on the app folder to get inside so you are in the app folder, Right click the actual app in winscp and click properties: like this:
6 You should get a window like this after clicking properties:

7 Check the boxes exactly the way on the picture and it should set it at 0755, hit ok
8 Now reboot the iPhone/iTouch and it should turn on with your new app ready to go!
If I have forgot something or you have questions post below!