Syncing Apple Devices

Assuming they are your devices, sign into iCloud on all 3 using your Apple ID. On the iPad and iPhone then go to Settings/<your name>/icloud and turn on all of the switches. If your computer is a Mac go to Menu/System Preferences, iCloud and do the same thing there. If your computer is Windows get iCloud for Windows from this link-->Download iCloud for Windows - Apple Support.

On the iPad and iPhone, see the options in Settings > [username] > iCloud (e.g., Contacts, Notes, Calendars, etc.)

On the Mac, see the options at Apple menu > System Preferences > iCloud.

More information on syncing photos and files is in:

Set up and use iCloud Photos - Apple Support

Set up iCloud Drive - Apple Support