Once you are in the root folder, select the set in which the item you want to publish resides.
Click on Publishing Properties which will open a dialog where you can set the path to save the file.
After setting the path location, you are ready to publish so you can click on the "Publish" button in the Navigator.
When you select the publishing path for one item in a specific set you are applying this setting for the whole set, so all other items in the same set will be published to the same location (until you change the path again).
You can also create a Publisher Set in which there is only one layout to publish.
If you press Publish without defining the destination path beforehand (the Path field is empty in Publisher Set Properties), an automatic warning will appear asking you to define a path for your publication.