The SCA, according to its governing documents, was formed for the purpose of "Research and education in the field of pre-17th-Century Western Culture." This explains why people who actually attempt to do research and education are called "authenticity Nazis", and why we have so many Japanese personas and Cavaliers running around.
Just kidding, of course. The truth is that those documents were written for the sole purpose of obtaining tax-exempt status, and bear no relation to what the SCA really stands for, which is to smack each other with sticks and drink ourselves into a stupor, not always in that order. But to keep up appearances, so that we can keep our Board members from going to jail for tax evasion, we occasionally participate in an activity known as "The Demo".
Now, The Demo comes in several forms. One of the more popular ones is the Movie Demo, in which the local group visits a movie theater, inside of which is playing a film that takes place during the SCA's period, such as "A Knight's Tale", "The Messenger: The Story of Joan of Arc", or "Star Wars: The Phantom Menace". The purpose of the Movie Demo is to stand around in garb, and give the theater's patrons something to gawk at before we go in to see the movie for free.
Another kind is the RenFaireDemo. For the RenFaireDemo, thirty or so members of the local group are permitted into the RenFaire, where they set up a small booth. The SCA members then take turns staffing the booth in pairs, while the other twenty-eight go and enjoy the RenFaire for free. This is often combined with:
The Membership Drive Demo. These Demos, often held at large flea markets, air shows and public executions, are held for the express purpose of attracting new members into the local group. They're held by Cantons that want to be Shires, Shires that want to be Baronies, Baronies that want to be Principalities, and Principalities that want to break away from the East Kingdom.
Of course, in order to swell our ranks, we have to make ourselves enticing to potential members (or "marks", as they are sometimes called). We put on our very best T-tunics and sweatpants - the ones without too many holes - and perform entertaining activities like fighting, fencing, and beating up sports team mascots. Our ladies lay out their best garb and embroideries for sticky-fingered children to besmirch with grime, and our men bash each other with sticks as the marks scoff, "I could do that," in voices loud enough that their girlfriends will hear them, but soft enough (they hope) that the fighters won't.
And then we gently lead the mark towards the Brochure Table, where the person sitting there coerces the mark to write down his name, phone number and address. The mark is then given a number of flyers and pamphlets, all of which make the claim that the SCA is all about research and education in the field of pre-17th-Century Western Culture.
Upon reading this, the mark runs back to the table and scratches out his name, address and phone number, because he was hoping to find a group where he could smack people with sticks and drink himself into a stupor, not necessarily in that order.