The purpose of this volume is to provide information necessary for successful operation of the FLAG code. Section 2 provides instructions for the preparation of data input to the code. Section:3 discusses the output which results from a FLAG run. Section 4 is intended to aid the user by providing detailed descriptions and flow charts of the subroutines in FLAG. Definitions of variables are also included in this section. The auxiliary programs which have been written to produce graphics from the FLAG output files are described in Section 5. Two sample runs. a cold flow and a hot flow case. are discussed in Sections 6 and 7. respectively.