Enter Recovery mode by turning off your iPhone or iPad, then holding the Home button (on the front, below the screen) on your iPhone or iPad. This can take a while, so don't give up after a few seconds.
When it says 'Connect to iTunes', do exactly that - plug it into your Mac or PC and open up iTunes.
iTunes will tell you that it's detected an iPhone or iPad in Recovery Mode, and that this needs to be restored - click OK to agree to this, and then Restore iPhone or Restore iPad (as appropriate).
Finally, choose the option to Restore and Update. iTunes will download the latest version of iOS 10 and install it on your Apple device.
Backups are never backwards compatible with iOS.
The backup may not be from a version that is higher than the version you want to restore it to.
So, no, iOS 11 backups can not be restored to a device with iOS 10 on it.
Neither can you restore a backup from 10.3.3 to 10.3.2 for that matter.