I'm using the iPad with retina display and have an iPhone 5. I've already bought quite a few apps on my iPhone that I thought would be transferable since they were iPhone/iPad apps, but when I go to the purchase portion in the app there is nothing there on my iPad App Store and if I go to the app that I have already paid for before, it says that it still cost money. I don't quite understand. Does anyone have any pointers or advise? Any would me appreciated at this time. Thank you!
If an app has a little + sign by the download button, then it's a universal app and scales up or down to suit whatever device it's on. they'll look good on both ipad or iphone.
You can put phone only apps on an iPad, you'll just see this little X2 button when you open the app, asking if you want to keep it phone scale or if you want to 'zoom in' to ipad scale. Some look good, some don't. All depends on how good the resolution was on the original app.
I had a Touch and when I bought my iPad, I put all the touch/phone scaled apps onto the iPad, Some I kept, some I did not. Some I have tolerated a bit fuzzy because I didn't want to rebuy them, others I purchased the iPad version.
But as long as you use the same apple ID, you can use the same apps (the biggest caveat, while you can put phone ones on the ipad, you can't put ipad ones on the phone)