2.1. The Tendril

Select the Line tool and draw a long line as below.

You can adjust the end widths using the Radius sliders on the Object Properties Panel, and you can increase the Resolution using another slider in case the model has sharp corners.

N.B. When "Radius B" is set to zero it matches "Radius A" to make an even sized tube. When you move "Radius B" off zero it starts making more cone shaped curves.

2.2. The Belt Buckle

This tutorial combines a Line with a couple of mesh edits to make an evolved model.

Choose the Create Line Tool and draw the curve below in the Front view - taking care to overlap the centre line.

N.B. I have exagerated the centre lines of the grid to make them easier to see.

Next adjust Radius A to thicken the Line.

Now for the mesh tools - pick from the menus at the top of the window "Mesh/Mirror".

Mirror always works in the front view across the grid centre line.

Next switch to the Perspective view and rotate the view (Shortcut: Hold Alt + drag left mouse button)

Choose the Scale Tool (Shortcut: Press 'R').

You should see a colourful manipulator with little cubes at the ends.

Drag the blue cube towards to squash the mesh along the Z-Axis (Front to Back).

Here is the finished buckle in 4 views. Note how it is flattened out.