What Does “Too Many Cooks in the Kitchen” Mean?

We see in this cartoon a group of people sitting around a conference table, most of them with chef’s hats on, the tall hats sometimes worn by the main cook or “chef” in a restaurant.
The man leading (running) the meeting announces that they have “too many cooks in the kitchen.”
This cartoon is related to an old expression in English, “Too many cooks spoil the broth.” To spoil something means to ruin it, to make it so bad you can’t use it. Broth is a liquid usually used in making soups.
The original expression, then, says that if you have too many cooks in a kitchen, the result will be bad food.
The more general idea is that you can’t have more than one boss, one leader, in any project. If you do have too many “leaders,” things won’t turn out well (have a good result).