Consonants may be voiced or unvoiced. When a consonant is voiced, your vocal cords are engaged while you are altering the airflow; if it is unvoiced, your voice is not engaged.
When you look at the chart, you will see that there are often voiced/unvoiced pairs at different points of articulation. Three pairs in English that help give an idea are [s] and [z], [t] and [d], and [f] and [v]. Each of the pairs have the same place and manner of articulation, but in each pair, the first sound is voiceless and the second is voiced. The voicing changes the meaning as in the following pairs of words. They are spelled differently, but the pairs sound the same.