G after N means that the sound is nasal. It{s similar to the pronunciation of gerunds or adjectives in English: ridiNG., amaziNG.

have or have not a "g" is quite different. and all "g"s in chinese PinYin are not silent when a chinese PinYin star with "g" , such as ge1 (哥，means brother),its pronunciation just like give or big in english but when a chinese PinYin end with "g", such as jingren12【not 14】(惊人,means amazing.).it kind of different。 here, "g" can not be separate from "ing"(also ang 、eng 、ong） ah~it hard to explain pronunciation that we can not hear each other. I give you some example,wish you understood.. "JinTian"11(今天，means today) if we use The International Phonetic Alphabet,it should be [tɕin,tʰiɛn] and Jingren12 ,it should be[tɕiŋ,ʐən] see? "in" pronounce in,but ing pronounce iŋ. "in" sounds like english prep.:in but "ing" sounds like "en" in english word :English or "ing" in reading when you pronounce "ing",compare with "in", there are more nasal sound ... wish you understood.and the easy way is you can find some videos that teach people how to pronounce Chinese Pinyin....