Q: incorrect apple id or password

Have you tried restarting your iOS device and resetting the settings?

Check these articles and follow the instructions.

If you forgot your Apple ID  - Apple Support

If you forgot your Apple ID password  - Apple Support

https://iforgot.apple.com/appleid

After you change the Apple ID, follow these steps:

OS X El Capitan - Technical Specifications

Hi D. Cohen,

Thank you for your reply. Yes, I have, but every time I try to sign in to either iTunes store or iCloud using my current Apple ID, it keeps saying incorrect Apple ID or password. My Mac didn't have a problem, just my iPhone and iPad...

Is this something that just started happening recently?  Have you changed your Apple ID recently?  Are you the ORIGINAL owner of your iOS devices?

On you iOS device, try signing out of the iTunes Store & iCloud and then sign back in.  If that still doesn't work, try resetting the device (hold down the home & sleep buttons until the Apple logo appears) and then try signing in again.