In spoken American English there are many pairs of consonant sounds that are articulated using the same tongue and mouth shape. The difference between these pairs of sounds is that one sound is voiced and the other is voiceless.

Voiced sounds cause the vocal chords to vibrate. Voiceless sounds are softer and do not cause the vocal chords to vibrate. Here are a few examples:

In spoken English the /s/ & /z/ sounds employ the same tongue position and mouth shape but the /z/ is voiced and the /s/ is voiceless.

The English /k/ & /g/ sounds are both produced in the back of the throat but the /g/ is voiced and the /k/ is voiceless.

The /p/ & /b/ sounds are both made by pushing your lips together and then releasing them but the /b/ is voiced and the /p/ is voiceless.

Many non-native English speakers used the voiceless sounds /s/, /k/ & /p/ when they should use the voiced sounds /z/, /g/ & /b/. Making this type of pronunciation mistake will both contribute to your accent and cause misunderstandings.