There is an easy way to crimp the edge of an empanada - just by using the tines of a fork. This can be a good method for appetizer-size fried empanadas. In fact, a fork-crimped edge is so common on fried empanadas that when you see an empanada like that, you can almost assume it's fried. The traditional braided edge, or repulgue, is more common on baked empanadas.
The type of braid and shape of the empanada can let you know what's inside, if you know the code of your particular neighborhood bakery. Bolivian-style empanadas, called salteñas, are braided along the top, rather than the side. If you see an empanada braided along the top, be aware that it might have a very runny filling. Salteñas are famous for their liquidy fillings, which is good to know before you take a bite and it all runs down your arm.
To fold the repulgue, think of triangles. Start at one corner of the empanada, and fold a triangle of dough from the seal edge down over itself. Press down to seal it, extended that part of the dough a bit as your press on it, and fold down a second triangle right next to the first. Press it down to seal and repeat, continuing all the way around the edge. The last triangle can be tucked underneath the edge if necessary. Some people like to pinch and fold the triangles between the thumb and first finger of one hand while cradling the emapanada in their other hand.