The letters b, hard c, d, hard g, k, p, and t are plosive consonants and when pronounced, they push out a lot of air. On condenser microphones (which are the microphones of choice for voice over work), a puff of air from a plosive consonant may produce a bassy “pop” in the middle of the delivery, which can be an annoying distraction.
To avoid this problem as much as possible, we use a windscreen, which may be a porous foam sleeve over the microphone, or a double windscreen inserted between the performer and the microphone. These serve to divert the puff of air from a direct line to the microphone and soften the plosive.
You can learn to deliver plosive consonants directly to the microphone without popping by practicing your delivery four or five inches in front of a burning candle. It may take many hours of practice, and you may have to relight the candle countless times, but over time you will adjust and learn to deliver plosives without blowing out the candle. Then, when you work close to a microphone, you will be able to avoid popping entirely.