To speak of the word 'God', means we have an concept of Him. So therefore this concept is understood, and so is God.
'God' means many different things to different people. To have so many often conflicting ideas about a single concept surely means that concept is not understood. The concept of a Square for example is understood, it's a shape with four sides of equal proportion. The concept of god is not understood.
To understand the existence of god not only means understanding the concept, it also means that he exists. Which does not follow from the claim.