Lost Mail icon on iPhone. How do I restore it?

I lost today my mail icon. After trying shutting the phone off I could not get it. In the settings it was also missing. Next I tried the App Store and I "downloaded" it. Then I got a welcome screen. Tried to sign into a gmail account and got a message telling me it was already there. I was also missing my company email file. Tried resetting the home screen as someone suggested and did not do much. Finally I went to settings, found the mail settings restored and went into accounts. All my mail accounts were there but they had been turned off. I turned them back on and I seem to be back to normal.