App Store vs iTunes vs Apple ID, vs iCloud"

Is the password I use for signing into the App Store the same password as for iCloud? Since being prompted to make the iCloud email address upon getting my first iPhone a few years ago, I have never had to sign into anything iCloud specific (that I know of).

Now I want to sync my calendar to the Outlook App on the iPad and I think I have to add the iCloud account & I don't know what password to use. (Their instructions are sorely lacking)

I Really don't understand the difference between my accounts and password and/or sign-in credentials at: App Store vs iTunes vs Apple ID, vs iCloud

Surely I can't be the only one whose mind is befuddled with these concepts. Much thanks to whomever can provide clarification on this topic.