There are a couple of ways of closing the curve. If you are creating the curve from Flexi Draw, press shift + space at the last point to close it. Or you can use the Close Splines (or Close Splines with Straight Line depending on your requirement) tool from the Other Tools section in the Bezier Utilities panel.
To make a planar object from the curve, use the Convert Curve to Mesh tool. I guess, the options in this tool are self-explanatory. But just let me know in case you face any issues.