The Say () for () Secs block is a Looks block and a Stack block. The block give its sprite a speech bubble with the specified text - the speech bubble stays for the specified amount of seconds. This block is identical to the Think () for () Secs block - except that this block gives a speech bubble, while the other gives a thought bubble.
As this block gives a sort of speech, the block can be used whenever a conversation takes place. Another common use is when unpredictable text must be shown - it is an easy alternative to stamping characters on the screen.