To create a curved line, start by creating a line. Don't press enter yet.
Next, use the option Curve Left or Curve Right. Note: Click on the Curve for it to change to either the Right or the Left. You can also scroll on your mouse wheel as well!
Click "OK" or hit enter on your keyboard to lock the curve in place and continue sketching the rest of the shape.
You can edit the size of the curve by using the option provided.
Click here to watch the sketch tool in action!