MMMmmm that's a nice snake.
Q: How do you make a smooth curve with a pen?
Using the pen tool, hover the cursor to a desired starting point for the line, then drag to create "handles" for the anchor point. Do this again and you get a curve.
Q: How do you make a point (line) with the pen?
Just click to a desired starting and end point, creating a straight line.
Q: How do you make a smooth curve with the curvature tool?
Just click to a desired starting and end point. This will create a b-spline-esque line automatically.
Q: How do you make a point (or a straight line) with the curvature tool?
Unless you're creating a single line, hold alt, then click to a desired starting and end point. This will only create a straight line.