The 1st tool is the Simple Curve tool which creates a curve between 2 points:
The 4th tool is the Curved Parth tool which will create a curve by selecting a number of points (more than 2) and create the curve touching the various points:
The 3rd tool is the Curve tool which uses point as control handle and is a curve between 2 points… This tool is a little more complicated to use as you need to make a control point on the inside of the 2 points that you wish to connect with a curve, at the correct angle and length to create the curve that you require:
And the 6th tool, the one that you used above, is the Tools for creating curves tool. For each curve between 2 points you need to create extra points - at the correct angle and length - for the curve handles to connect with so that the curve is how you wish it to be:
I hope that this helps you. You will find this described in the reference manual in the Wiki (the link is at the top of this page).
And here is the link to the French manual: https://static.miraheze.org/seamlywiki/f/fa/Seamly2D_Manual_-_French_A.pdf