Strictly speaking, it is impossible to give an exact and detailed description of a sound within the limits of a short definition, because not a single sound is pronounced identically even twice. Sounds undergo changes due to the individual manner and even mood of the speaker and due to the complementary distribution in which every sound exists in the language.
The first step to learn a sound is to isolate it. It means that for teaching purposes we single out the principal, or typical variant of the phoneme as a segment of the system, which is conventionally free from any influences. Then a detailed description of this variant should be carried out by means of simultaneous comparison with the similar sound of the mother tongue. The next stage is the mastering of the sound, which is done by teaching the students to pronounce the sound in a definite set of contexts in which this sound occurs. The