From BlenderWiki

This panel appears in the Editing Context panel group which is accessed using F9 or clicking button in the Buttons window. In the following, U applies to curves and both U and V apply to surfaces. See Nurbs for further usage of this panel.

[edit] Curve Tools

• Poly - Convert selected curve to a linear curve or polygon. (Bézier Curve only)
• Bezier - Convert selected curve to a Bézier curve. (Bézier Curve only)
• Nurb - Convert selected curve to a Nurbs curve.
• Set Weight - Nurbs curves have a weight per handle; the extent to which a handle participates in the interpolation. This button assigns the Weight value to all selected vertices.
• Uniform U - Sets the knots to create a uniform distribution. Use this for closed curves or surfaces.
• Endpoint U - Sets the knots so that the first and last handles are always included.
• Bezier U - Sets the knots table in such a way that the NURBS behave like a Bézier curve.
• Order U - The order is the 'depth' of the curve calculation. Order 1 is a point, order 2 is linear, order 3 is quadratic, etc. Always use order 5 for Curve paths. Order 5 behaves fluently under all circumstances, without annoying discontinuity in the movement.
• Resol U - The resolution in which the interpolation occurs; the number of points that must be generated between two vertices in the curve.
• Weight - The weight that is assigned with Set Weight.
• 1.0 - A preset. A number that can be used to create pure circles and spheres.
• sqrt(2)/4 - As above.
• 0.25 - As above.
• sqrt(0.5) - As above.