Q: i want to purchase an app for my father

You can gift apps to other people : http://support.apple.com/kb/HT2736

But it's not currently possible to gift ibooks, though you could gift a gift card or certificate (if they are available in your country) and suggest that he buys that book with it

If the app is eligible to be gifted, you can.

Tap on the app in the App Store and when the app description pops up - tap on the Arrow in the upper right corner and Gift will appear as an option. You can only gift an app in your country fro use in your own country.

There is also an iTunes gift option in the App Store right now. It is called appropriately enough iTunes Gifts. Tap on it for options of gifting different denominations of iTunes credit.

These options are available in the U.S. store, I can't speak about other countries.

Uh.... You're quite welcome.