You can create or edit curves by using curve functions in "Curve Ribbon Bar".
Groups in Curve Ribbon Bar:
Direct Sketch: draws curves by creating a sketch.
Creates spline through defined points. You can change positions of points or drag points while the command has been activated. You can create 3D splines
Draws a line between points in the model without creating any sketch. Also, you can draw lines by angle or vector by changing end options in the command