There is no need for you to undertake the restoration from the backup file yourself. This will be done automagically as part of the boot process (unless you use a boot code like 'base' or 'norestore'), provided the 'tce' directory was "recognised".
As the concept pages (and the FAQ page) are highlighting: when using USB drives one needs to use boot code 'waitusb=n' (where 'n' is a delay in seconds) to ensure device recognition. A simple check to see whether a device was identified is via cat /opt/.tce_dir If that still shows the (default) value of '/tmp/tce' not device was found, and your TC system remains therefore in "cloud mode".
If you struggle with the documentation, please raise specific questions re. those parts that are hard to understand. The Core team is in my experience quite keen to ensure improvements are done where they seem required. A claim along the lines of "... I don't understand the concept page ..." does not help anyone, as it is way too generic.