The consonants in Hindi are arranged into groups according to where they are produced in the mouth. It’s worth noting that even if you cannot clearly distinguish the sounds when you hear them you should be able to feel whether you yourself are producing them in the appropriate place. This group of sounds are all pronounced with the sound generated in the very back of the mouth.
for कान nm. ear. क is similar to the k in speaker. There is less breath expressed when saying क than is normal with k in English which is normally semi-aspirated.
for खाना nm. food. ख is the aspirated form of क. To check if you are aspirating this consonant place your hand in front of your mouth when you pronounce it. You should be able to feel a breath of air when you say it.
for गाय nf. cow. ग is similar to the g in go. It is a voiced sound so your vocal chords vibrate as you say it, which distinguishes it from क.
for घर nm. home. घ is the aspirated form of ग. Like ख you breathe out while saying it. This character has its top closed by its head stroke, distinguishing it from ध which comes later in Devanagari script.
for अंगूर nm. grape. ङ is similar to the ng in king. It does not occur at the beginning or end of words and occurs only as an ‘n’ sound immediately before: क, ख, ग and घ.