INSERT is used to bring something very small into full frame, for example a letter, a newspaper ad, a sign, a box of chocolates. It is not used to insert quick shots into the action and also not for bigger objects like a television. An INSERT should be followed with a BACK TO SCENE unless a master scene heading or a secondary headings follows anyway.
Directions like INSERT disturb the flow of reading so it is good advice to use them sparingly. For example, the following INSERT is not such a good idea:
INSERT - COLT .45 AUTOMATIC ON THE TABLE
BACK TO SCENE
This works just the same: