This report documents the use of the CELC3D computer code for the computation of two- or three-dimensional unsteady currents in coastal, estuarine, or lake waters based on the free-surface model described in detail by Sheng. The present version of the code is implemented on a VAX 11/780, a virtual machine. It therefore contains no buffering scheme and is programmed to run entirely in the central memory. Since it has no buffering scheme, it contains no machine dependent input/output and, except for minor program changes, should run on any other virtual machine, e.g., the CDC cyber 203, or other non-virtual machine with sufficient memory. The CELC3D program solves the mean equations of fluid motion within a water body with respect to a right-handed Cartesian coordinate system located at the nominal water surface. These equations consist of the partial differential equations for surface displacement, vertically integrated velocities, three-dimensional velocities, temperature, salinity, density, and sediment concentration. The equations of motion are solved in dimensionless forms and are given in Appendix A in detail. The major variables and their corresponding FORTRAN names are given in Appendix B. Sheng presented numerous example calculations of the CELC3D model, including: tidal currents in an open bight, wind-driven currents in a shallow lake, wind-driven currents in an open channel, formation and deepening of a thermocline, and tide- and wind-driven currents in the Mississippi coastal waters, etc. This report, for simplicity, only briefly presents the application to Mississippi coastal waters.