If you only want clear curves without fill, select the object and edit its style; go to Object > Fill and Stroke...
You'll see a popup with settings for Fill and Stroke, choose the Fill tab and click on the first left button (X means no paint).
There are more ways to bring out that popup, there's a button on the top toolbar for it, or click on the Fill and Stroke boxes you see in the bottom left corner of the window.
If you want to draw curves without fill right away and not have to change it later;
1. select Pen tool
2. look in the top right corner of the window, you'll see Fill and Stroke boxes, click there and you'll get an option to set the default setting for drawing curves, you may have to set it from an existing object
Judging by your image I think you didn't quite follow the tutorial exactly. This is what I think you did:
1. the same as tutorial
2. the same as tutorial
3. the same as tutorial
4. drag to here, DON'T RELEASE
5. hold SHIFT
6. move handle upwards, RELEASE
Point 7 is like point 3 etc
16. drag to here, release AND CLICK RIGHT MOUSE BUTTON to finish
This is what the tutorial says you should do:
1. click and press here
2. drag to here, release
3. click and press here
4. drag to here, RELEASE but don't move pointer
5. press SHIFT and then press (left mouse button)
6. move upwards (still holding SHIFT) and RELEASE both Shift and mouse
7. same as 3.
etc
.
.
16. drag to here, release, right-click to finish
This is the result you should get from the second tutorial:
