The Build menu

Compile: Saves and compiles the current .mos (Mosel) file. If there are compilation errors, they will appear in the Info Bar. If compilation is successful, the entity tree will be populated with entities from the model.
Run: Saves, compiles and executes the current .mos (Mosel) model. During the execution, the output from Mosel will go to the Output pane from the Run Bar. After the run terminates the entity tree will show actual values taken by variables in the Mosel model.
Pause: Uncheck this option to resume the execution after it has been paused.
Stop: Attempt to interrupt the execution of a model or an optimization by requesting that Mosel and the Optimizer stop. Mosel/the Optimizer will stop whenever it is safe to do so.
Options...: Shows the Run options dialog, allowing the user to change settings for Mosel or Optimizer runs. It can also be invoked while a Mosel model is executing or during the optimization of a matrix file. Changes will take effect immediately after the dialog is dismissed.
Export matrix...: Shows the Export matrix dialog for exporting matrices produced during Mosel runs to LP or MPS files.