It would be easier as a notebook entry, but: This exhibition explains earth as an important building material used in the countryside[1] in Moravia. The main focus is[2] on traditional techniques used to build the walls of mud buildings. This extinct tradition is represented mostly by disappearing building on the ground[3] The exhibition unveils a little of the easy yet effective building techniques of the bygone generations and bears an important witness to their lives. [1] Using countryside is a little clearer, as it almost reads as country of Moravia. You could also write 'rural areas of Mor..; [2] Maybe a little more natural phrasing. [3] Is not at all clear - I don't know what you are trying to write. Do you mean that the only evidence of these techniques is the ruins?

A slight correction to my answer :) it is [!] sign. sorry This exhibition explains earth soil[1] as an important building material used in the country of[2] Moravia. The main stress is put on traditional technique[!] used to build walls of mud buildings. This extinct tradition is represented mostly by old, fading buildings [3] on the ground. The exhibition unveils an[4] easy yet effective building technique of the bygone generations and bears and important testimony [5] to their [6]way of life.

I'd write it like this: This exhibition explains earth soil[1] as an important building material used in the country of[2] Moravia. The main stress is put on traditional techniques used to build walls of mud buildings. This extinct tradition is represented mostly by old, fading buildings [3] on the ground. The exhibition unveils an[4] easy yet effective building techniques of the bygone generations and bears and important testimony [5] to their [6]way of life. I put my corrections in brackets [] and I hope I helped you out. Cheers