You install an iPhone app on an iPhone, and an Android app in an Android phone.
Just visit the appropriate app shop or market on your phone, find the app, choose it, pay for it if necessary and go forward with the installing. That's the same for all apps.
http://ipad.about.com/od/iPad_Guide/ss/iPad-101-New-Users-Guide-Install-Move-Delete-Folders_4.htm shows how to do with an iPad.
I would like to install top Indian social network "bharatstudent.com" [www.bharatstudent.com/bsmobile.php#1] iphone apps, android apps in my mobile. But I am unable to understand that procedure, If you have any idea about installation of apps in mobiles, please suggest me step by step.
Thanks in advance