Typically used with: Presence.
In short: make smiles and money. All the world's a stage and you're the star — or so your prima donna attitude would suggest. Characters with ranks in Perform are "the talent", and are superbly good at entertaining others. Such a trade can be used to lighten moods, make some cash, and create diversions.
When you buy a rank in Perform, your character also gets the added bonus of learning a new performing art (e.g. tuba, dance, singing, mimicry, juggling, comedy). Ask your GM if a particular performing art is applicable in your campaign. Usually, you'll need to be trained in an art of performing if you want to make effective use of it for the purposes described below — it's hard to move hearts when you stink at the clarinet. Ranks in an Occupation specific to a means of performing (e.g. violinist, comedian, actor) are always applicable to Perform rolls involving that talent, and obviate the need to buy a rank in Perform to learn the talent.
A Perform check can be used like a Negotiate check to improve someone's mood: for example, sing a beautiful, happy song, or tell a hilarious joke. See the Negotiate entry for the DLs for such a use. The GM may rule that a particular character may not be able to be affected by the performing arts, particularly those with little emotion or no sense of humor.
A Perform check can also be used to score some quick wages in a populated area. Money received is not only a product of how well you Perform, but also the economy of the city or town in which you do it. Usually, a minstrel can entertain for an entire evening and earn an amount of wealth equal to the check rolled.
The GM should make it apparent that a great amount of attention (both good and bad) can come from higher Perform checks.
A character can use Perform to create a diversion. Take for example a minstrel who sings a song on a street corner while his ally picks the pockets of the audience. Any person enthralled by the performance (i.e. loses a Discern to the Perform check) takes a −2 to their Perception to notice the Thievery.
A Perform check can be retried, but usually after one unimpressive performance, you may be too busy dodging tomatoes to give it another shot.