A model file is a Powerlines Pro unique design file, at any time your model can be saved as a .power file so that it can be physically saved to your device or passed on for someone else to view.
To import, simply open "Import from model file" from the Project menu and select your desired file, this will automatically import the design. If it is being imported into an existing design, you will have the option between adding the data to existing, or overwriting it.
To export, simply click "Export to model file" and it will export as filename.power. To do this, select the 'Project' tab in the menu and then click export to model file. This will automatically download your project as projectName.power.