The difference between a clause and a sentence can be difficult, but important. A clause basically must have a Finite whereas a sentence is just an orthographic convention beginning with a capital and ending with a full stop. Here is a text from SMH that illustrates this difference nicely:
When designing their own home, architects Sacha Zehnder and Jaya Param of Walk North Architects were reminded regularly they’d chosen ”the most difficult block” in the area.
Steep, tree-covered, 50 metres above sea level, with no road access; and, on idyllic but somewhat logistically challenging Scotland Island, in the middle of Pittwater and accessible only by boat.
Here the first part actually contains three clauses in one sentence: a mental Process (‘were reminded’) and a projected clause (‘had chosen’) plus a hypotactic ‘when’ clause. The second part, on the other hand, is a ‘sentence’, in that it begins with a capital and ends with a full stop, but is not a clause as there is no Finite element. I think the second sentence is, in fact, a kind of logico-semantic relation of enhancement giving reasons why the area is ‘difficult’ (although I guess you could also it’s elaboration – exemplifying the ‘area’).
I think a lot of EFL students might miss the logico-semantic link between the two parts if they are not familiar with the difference between ‘sentence’ and ‘clause’.