The arc tools in the Sketch > Create panel let you create different types of arcs as sketch geometry or construction geometry in an active sketch in Fusion 360.
3-Point Arc 
You click to place the start point, place the end point, then place a third point that lies along the arc.
Center Point Arc 
You click to place the center point, place the start point, then place the end point. Alternatively, you can specify an angle value.
Tangent Arc 
You click to place the 2 end points. The arc will maintain tangency with the geometry it connects to at each end.