For example: going, dancing, shaking, clobbering etc.
In the end of these words are "g" letter. So do I need pronounce them when I talk?
there are three pronunciations of the suffix "-ing" you will hear.
This is the standard pronunciation. Note that the sound [g] is not pronounced. You can think that the letter "g" alters the pronunciation of the letter "n". /ŋ/ is a sound articulated similarly to the sound /n/, but the tongue touches your soft palate instead of your alveolar ridge.
This is /n/: http://upload.wikimedia.org/wikipedi...olar_nasal.ogg
This is /ŋ/: http://upload.wikimedia.org/wikipedi...elar_nasal.ogg
It's a non-standard pronunciation. Note that while native speakers do say [ˈgəʊɪn] for "going" (and sometimes write goin'), but they will not say [sɪn] for "sing". "Sing" always ends in [ŋ].
A non-standard pronunciation too. Perhaps [ɪng] is possible too but I don't remember having heard it.
I should have specified that I was not suggesting that a voiced hard "g" should be pronounced with "-ing", simply that the common pronuncation of just "-in" should be avoided.
"I'm doing that" should sound as it's written, not like "I'm doin that".