Wait for the process to complete (don't turn off your Mac!
) and after the final reboot, Mac OS Sierra should be up and ready for use.
This will allow you to copy and paste between Macs and i OS gadgets like i Phones and i Pads.
It’s fairly common for computer users to delay updating to major operating system releases, and though Mac owners tend to be a bit better at upgrading than Windows users, many are still running old versions of OS X.
For some users there are good reasons for this, maybe lingering on outdated OS X versions like Snow Leopard because of compatibility issues with a specific app, or because they just really like it.
These applications include Apple's own productivity apps like Maps, Pages, Numbers, Mail, etc.
This is great for jumping between multiple tasks within the same application without exiting your current place in another window.