I'm having trouble to differ 'n' and 'ng'. I've been searching it on internet, but I can't really differentiate them. How can I pronounce them correctly?
This answer provides a useful explanation and also explains what to do with your mouth when pronouncing the two sounds. As that commenter mentioned, my wife is from Jiangsu and even in English can't distinguish between the two sounds.
This youtube video has some concise examples from English.
This youtube video has some Chinese examples although the audio quality and the pronunciation aren't very clear. It's the best I could find.
N and NG are both nasal sounds. The difference is also found in English. The air does not escape from the mouth(as it is blocked by the lips or the tongue) but the nostril.
When pronouncing ［n］, put your tip of tongue onto thre upper gum. Let the air come out from the nose.
When pronouncing ［ng］, low your back of tongue, then the air will escape from the back.
Are you looking for help with Mandarin or English?
In American English, /n/ is made by pressing the tongue against the alveolar ridge (this is the roof of the mouth, behind the teeth). We also make the t, d, and l sounds with the tongue in this location. For/n/, you need to completely seal the tongue against the roof of your mouth in the front.
The "ng" /ŋ/ sound is also made by sealing the tongue against the roof of the mouth, but with the back of the tongue rising up to the make the seal, the the front of the tongue down. The k and g sounds are also made in this location in the mouth.
You can get even more detailed help to differentiate the n and /ŋ/ sounds in this video: