A view-only wallet sees the payments you receive but can’t spend anything. Use one on a second computer, to watch donations, or for your accountant.
Wallet › View-Only shows the three things a view-only wallet needs: the primary address, the secret view key and the restore height. Create view-only wallet saves one as a file, with a password if you want; Show QR shows them as a QR code for another computer.
On the other computer, choose Restore wallet from… › Keys, set the wallet type to View Only, and enter the primary address and the secret view key, or click Scan QR. Then enter the restore height.