Besides da classic "supposedly for giving schoolchildren practice/confidence in public speaking" action (but which actually scares
da crap outta many kids and/or causes lower-income students to feel jealous of da more-affluent ones who have nicer/fancier possessions to proudly display), this expression also refers to either of two "displaying da merchandise" actions:
(1) Where Person A lets Person B view one or more of
Person A's intimate body-parts --- with da understanding dat said reveal is supposed to be kept confidential, of course --- but then either Person A or Person B goes and
blabs about said private-area exposure to one or more other people, causing humiliation and/or repercussions to one or both "Persons", or
(2) Where Person A lets Person B view one or more of Person A's intimate body-parts in exchange for
Person B's verbally revealing to Person A one or more secrets dat he would otherwise not
divulge.
Example:
One good way to get a normally-modest chick to let you see her boobs/butt is to offer to help her with her homework or some other task dat she does not possess da knowledge and/or mental/emotional capabilities to tackle on her own, but insist dat she agree to a "show and tell" contract --- i.e., a deal wherein she agrees to let you view her "goods" in exchange for your putting in
da time/effort to tell her da
vital bits of info dat she needs in order to complete said
drudgerous task.