The SCA covers many things of interest to people who like history. So long as it happened before 1600BCE we probably cover it in some way!
We make our own clothes to fit the time our SCA character (persona) lived, and from other times that interest us. We do calligraphy and other forms of art. We try to understand what our ancestors knew about science. We cook and eat food from historical recipes, which is both healthier and tastier than most people think. We sing and play music, and we dance, and play games.
We also try to recreate the way people fought in the past, within the limits of not actually wanting to hurt each other. We fight with rattan sticks while wearing armour in styles that were used on battelfields, and with steel swords like historical personal defence weapons while wearing different armour. If the place we are meeting allows it we do archery, and we are very gradually working towards more things involving horses.
Events within the SCA range from a quiet sewing evening or a fight practice with a handful of friends, to a "war" with thousands. Locally most events are at the smaller end of this scale, but the SCA is a great way to make friends over much of the world and travel to meet them and play with them.
The SCA has an internal structure that very loosely resembles a mediaeval court, with the "King and Queen" changing regularly to the winner of a tournament, and "Peers" who are people who have excelled more than most in the things that we do. We also have officers who do the mundane work of running a society, like handling the money and keeping people's contect details safe. Everyone from top to bottom is a volunteer, and everyone is encouraged to pitch in to make things happen so we can all have fun.