I once came across a word that described how easy it was to guess how to use something without knowing what it was for.
The context was a blog post about a specific country, where the doors were either brightly decorated or painted in the same design as the rest of the room / wall paper.
They were often missing (traditional? western?) door handles, which meant that the visitor often did not know that they were actually doors or how to use them.
This was given as an example of something with low [missing word].
The rest of the post was about computer user interfaces (UI) or the user experience (UX) but I believe the word I'm looking for was a more general English word.
Update: Affordance serves my purpose for the missing word described above.
Best Answer
The word you're looking for is intuitive.
(Merriam-Webster):
However, since the British dictionaries I searched didn't contain this usage, I suspect that this word is used in this particular way primarily in American English.