How to download an app from itunes on my pc to my iphone 5c?

So I can't download anything from my phone so I want to do it from my computer. I bought this movie a while ago and whenever I try to download instagram to my phone an error pops up saying It can't download the movie but I don't want to download the movie. How can I just get instagram?

Go to the apple store.

I don't do Apple and I'm not some super expert phone person either. With Android you just plug you phone into the USB port and the computer just sees it as a flash drive. You can drag and drop files just like a flash drive. Now, I never actually did it with an app, but pictures and such it works just fine.