Ordinarily, our attention is directed at the myriad thoughts that appear in the mind sequentially. Sometimes these thoughts have clear and purposeful connections between them; at other times, the connections are tenuous and seemingly random. When we identify with these thoughts, and follow them, we experience the emotions that accompany them.
During meditation, with the help of the breath or any other suitable technique, we direct our attention to the mind in which all thoughts appear. That is, we observe, but do not follow, any thoughts that may appear in the mind, and simply note their arising, brief abiding, and cessation, without any emotional involvement. This is the practice of tranquility.