An arc is a portion of the circumference of a circle. It is named by its endpoints, There can always be three arcs. There is a major arc which is one that is more than 180 degrees, A semicircle which is an arc exactly 180 degrees, And finally, a minor arc which is one less than 180 degrees. A way to find the circles arc is to find the measure of a full circle which is 360. If you divide the arc by 360 then you get the fraction of the circumference that the arc makes up. Then multiply that length all the way around the circle by that fraction then you get the length of the arc.
A chord is a straight line that touches both sides of the circle. If you know the radius then you can draw a line connecting the two making a right triangle. From then on do the Pythagorean theorem.
Noah Lozano Geometry Blog 