Why I can't download an application on my iPhone?

Marking your own post as Solved may prevent others from trying to help because they think you have fixed your problem.

What happens when you try? Error message(s)?

See the Apple Support article(s) below.

Apps won’t downloaded.       

App Store, iTunes Store, or other Apple services - If you can't connect

Some things you can try. Do you have access to another WiFi network where you can try? That has worked for several people.

Try a restart.

Restart your iPhone, iPad, or iPod touch         

Try a forced restart.

Reset Device.      

Have not what?