Select Stokes(-Brinkman) from the pull-down menu and click the Option’s Edit… button to open a dialog to enter or edit the simulation options. Choose a Result File Name for the result file (*.gdr) fitting to your current project.

The parameters are organized under the tabs: Constituent Materials, Boundary Conditions, Solver, and Grid. The Equations & References tab gives a summary of the used equations and symbols which are explained in more detail here.