The Interpolate command requires that two database curves or boundaries be selected prior to being available. This command will create a new ruled type database surface. Database boundaries (u-min, u-max, v-min and v-max curves) are also created and are considered child entities to the ruled surface.
Select the database curves or boundaries from which to create the new surface, then Create, Interpolate. Adjust the Orientation if necessary. Click on OK to save the surface and close the panel.
There are a number of commands available on the Interpolate panel which are described here in detail. In the Orientation frame select the option which produces the best surface. Best aligns the curves to achieve the shortest distance between like curve intervals. Same connects intervals in the same order. For instance, low to low up through high to high. Opposite connects intervals in opposite order. For instance, high to low up through low to high.
Use the Tolerance frame to adjust the Fit Tolerance used by the Interpolate command for those cases where the default tolerance does not produce a pending database surface. In order to adjust the Fit Tolerance to a custom value, you must first uncheck the Use Default checkbox. Then simply type a new tolerance value into the Fit Tolerance text field.