When you've got your lines built, bent, and converted to fills, selecting the line with the white arrow will give you all the nodes along it's edge. You can only affect the curve from one node to the next, so we want less nodes to make life easier.
Although not necessary, I find it makes things easier to delete the nodes which describe the rounded edge, which I've highlighted in red.
After doing so, you'll have this wonky-looking rectangle.
Here you can see the effects of the bezier handles. The top right handle has been pulled out to make the right side bulge more, with a favour towards the top right (obviously). For comparison, the bottom right handle is in it's original position. Experiment with pulling the handles in different directions, and different distances, to see the effects. It's pretty intuitive, though.
I pull the right nodes across the left ones to get a pointed end, but the effect I had by pulling on the handles is still present. When you pull one node across another, however, the line will lose some of it's volume. It's a good practice to pull the handles out a bit before doing this step, so your line doesn't get too small, or disappear entirely. If done correctly, you should have only 2 points.
As you can see, each node has a handle for the left and right side of the curve. This makes it very simple to get exactly the line you want.
Now go forth, and make some clean, professional models!