Chivalry may well be the most important aspect of the SCA. It is what takes our game and turns it into the Dream. But what does chivalry mean to the SCA?
Since the Romantic explosion of the 12th century, the word 'chivalry' has referred to the moral ideals of the knighthood, including courtesy, honor, piety and generosity. In period, this ideal was meant to lesser or greater extents. That is what we attempt to recreate in our Society. But, of course, we recreate the medieval period as it 'should have been', so our chivalry is even more chivalrous. What this means is that while we accord respect to our (pretend) superiors, as knights of period were expected to do, but we also accord respect to our (pretend) inferiors, and to our equals of all stripes, regardless of gender, class, creed, religion or ability.
Chivalry in the SCA means lending a hand where one is needed, being kind to others, and respecting the Dreams of others. This is a place we go to get away from the real world. Ideally, it would be free of the arguments, discrimination, and hardships of outside life. In practice, this is very difficult to attain, but still we give of ourselves to make the Dream a reality.
What does this mean for newcomers?
In practice, this means be nice, or at least tolerant, to other people. Bow to pointy hats, carry where carrying is needed, and generally help where you can. No one will make you do this, but the generosity and helpfulness of the populace is what makes our Society function.