Intalling apps on iphone (ios 7)?

I have iPhone 4s (ios7) and it isn't jailbreaked. And i have to install some apps in the phone that i have downloaded from torrent.
but when i select the app which is to be installed on iTunes, the iTunes doesn't allow the installation of that app. What should i do. I don't want to jailbreak it.

If it's third party you can't use it on an apple product. It has to be apple approved, usually downloaded directly from the app store only.

Common sense lead me to think that it wasn't possible to install apps from other sources without jailbreaking, but a quick google search landed me at a few youtube videos.

Give this one a try, high like to dislike ratio generally means it worked for a high majority of the users, so it's safe to assume it should work for you too. I'm sure there are plenty of other similar tutorial videos on youtube.

Here's the video