The second five consonants -- च, छ, ज, झ, ञ -- are palatal consonants ( Palatal consonants). Palatal consonants are articulated with the top, flat part of your tongue against the hard palate -- the middle of the roof of your mouth. This is easier to understand if you slowly say the j in jump or the ch in change. When you start to form the j or ch, feel where the contact is between your tongue and palate. (It is useful to understand where the palatal consonants are articulated to better understand where the cerebral consonants are articulated. j and ch are common sounds for an American, but the Hindi cerebral consonants are not. Cerebral consonants are formed by curling the tip of your tongue backwards against the roof of your mouth, just behind where the top of your tongue was for a palatal consonant.)

च ca, /c, ʧ/

छ cha, /c^h, ʧ^h/

च is said with no aspiration, i.e., with no puff of breath when you say it. छ is the same, except said with aspiration. Think of the transliteration of च, which is just a c, as more equivalent to the English ch, i.e., not as in ceiling or cat. However, since I tend to aspirate ch, the ch in chair sounds more like छ.

ज ja, /ɟ,ʤ/

झ jha, /ɟ^h, ʤ^h/

ज is said with no aspiration, झ is said with aspiration. ज is like the j in judge.

ञ ña, /ɲ/

ञ is a nasal consonant. You'll never see it at the start of a word. You'll never see it on its own. It seems to appear only rarely in text.

I am archiving this information about the alphabet on the Hindi page: kirkkittell.com/language/hindi. More information from Wikipedia:

• Palatal consonants
• Sounds represented within /.../, e.g., /k/, are symbols of the International Phonetic Alphabet (IPA), which is extremely useful for me to understand how Hindi sounds.
• Sounds such as ka are transliterations from the International Alphabet of Sanskrit Transliteration (IAST). It's simpler to understand than IPA.