It's a little puzzle piece that says when the green flag is clicked and this is kind ; of like the beginning of a program; when you double click an icon on your desktop this is how something like that is implemented; it's listening for that double click, it's listening for that green flag.

是一小个按钮，它的意思是,何时点击绿色旗帜,这就好比开始运行程序;,当你双击桌面上的图标,就开始执行操作,桌面的图标需要双击，绿色小旗也等待点击来执行命令。

哈佛公开课 - 计算机科学课程节选

There's a little icon of a hand here, at top left, you go ahead and click that, and what happens is, we, the staff, see a little blinking icon in the top left that says one out of two hands, one out of 10 hands, or some number of hands, and it maintains in the little row up there your placement in line.

这里有一个小的手势图标，在左上角,点击它，我们教员，在左上角就看到一个小的闪烁的图标，这说明,两个人中有一个举手，10个人中有一个举手，或很多人中有人举手，并且它处于一行之中,那里你们布置成一行了。

哈佛公开课 - 计算机科学课程节选