I am having 1-Apple MacBook 2-Apple iPad Mini and 3-Iphone 6. How many Apple ID,s and iCloud accounts I need to create? Can a single ID can serve the purpose all the three devices?

Yes - you can (and should if you want them to sync iCloud information like Contacts and Calendars, and want them to share a Photo Stream, etc.) sign all of them on to the same Apple/iCloud ID.

Cheers,

GB

I just changed my AppleID and Password. They work just fine on my Mac, but my iphone 6 is not letting me sign in to Apps store and says that my AppleID is different than the real one (which is an email address). I got a confirmation email that my password was successfully reset, yet still isn't working for APP store. I went to accounts page online on my mac, and I just can't figure out what's up with my iphone 6. Should I contact Verizon? I just did and update yesterday...so highly suspicious that the update of my iphone caused a problem 😟

When you changed your Apple ID, did you sign out of the following on both the iPhone and Mac, and then sign back in with the updated ID:

iTunes & App Stores

Messages

FaceTime

iCloud

If you didn't, then you need to sign out of all services and then sign back in again with the updated ID:

Change your Apple ID - Apple Support

Cheers,

GB