The sounds b, d and g are in some sense cousins of the p, t and k sounds introduced on the first page. More specifically, b, d, g are the "voiced" versions of p, t, k.
What that means is that, for example, b is pronounced in a similar way to p (by stopping the air with the two lips), but unlike p, with b, you pronounce it with vocal cord vibration.
If you put your fingers over your Adam's apple and say the English words pay and bay, you should feel that in the case of pay, you don't feel the vibration of your vocal cords until after the aspiration (the "puff of air" accompanied by b, t, k in English that we mentioned on the first page). But when you say bay, you should feel your vocal cords vibrate pretty much as soon as you open your lips. You should notice a similar pattern with pairs such as tin vs din and Kate vs gate: in the first of each of these pairs, you don't feel your vocal cords vibrate until after the "puff of air"; in the second, there's very little "puff of air", and you feel your vocal cords vibrate pretty much as soon as your tongue lets the air flow through your mouth after the d or g sounds.
In English, although the vocal cords vibrate soon after you release the stop, they don't usually vibrate during the stop. In other words, when you say word such as bay, your vocal cords start vibrating almost immediately after you open your lips, but not while your lips are closed. Similarly, if you say the word abbey while holding your fingers over your adam's apple, if you're a native speaker of English you'll probably find that you feel vibration during the initial a sound, but that this vibration stops momentarily while your lips are closed for the b sound.
In French, on the other hand, speakers usually make the vocal cords vibrate even during the stop. So when a French speaker says a word such as abeille ("bee"), their vocal cords vibrate right through the word, even while the lips are closed for the b sound. Similarly, when a French speaker says the word dodo (which in French is an informal word for "sleep" as well as the name of the extinct bird), their vocal cords vibrate right through the word, even during the d sounds, whereas when an English speaker syas the word, their vocal cords essentially only vibrate during the o vowels.
On the next page, we look at so called fricative sounds in French.