Choose New Model... under the File menu or click on the icon in the toolbar. Note that creating a new model closes the current model (if any), prompting you to save any unsaved changes.
Choose Open Model... under the File menu, and then select the file to open in the dialog box. You can also click on the icon in the toolbar. Note that opening a model closes the current model (if any), prompting you to save any unsaved changes.
You can also quickly access recently used models with the Recent Models item in the File menu.
Select Save Model from the File menu, or click the icon in the toolbar. The first time you save a new model you will be prompted for a file name. Select Save Model As... from the File menu to save the model to another name.
Choose Close under the File menu. This will prompt you to save any unsaved changes.