Chocolate should be melted in the top of a double boiler over gently simmering water, never over direct heat.  Stir occasionally.  Chocolate scorches easily, so watch it carefully.

Or Chocolate may be melted in the microwave.  If chocolate is microwave on high, it may burn.  For best results, break the chocolate into small pieces and melt, uncovered, on med.  Stir occasionally and at least every min. near the end of heating.  Remove from the oven before it looks completely melted, then stir gently until smooth.

If chocolate comes into contact with water or steam while it's melting, it will seize, become lumpy and clump together.  If this happens, stir in the shortening, unsalted clarified butter of vegetable oil, 1 tsp. at a time, until the chocolate is smooth again.