Depending on the application you are using saving your project file will be different. Garageband, for example, automatically saves your project file for applications like Audacity you will manually need to navigate to File > Save.
If your application has an auto-save feature (usually found in the properties menus of an application), it is recommended to turn it on to auto-save every 15 - 25 minutes.
Saving your project file will allow you to continue editing your project at a later date.
Every platform will have a different way to share or export your audio project. If given the option, make sure your export settings match your timeline/project settings. Two common formats are:
In GarageBand on Mac, choose Share > Export Song to Disk.
To rename the exported file, select the name in the Save As field, then enter a new name.
Choose a location to save the exported file from the Where pop-up menu.
Select the format for the exported file. We recommend WAVE.
Choose the quality setting for the exported file from the Quality pop-up menu.
To export only the part of the project covered by the cycle region, or only the part of the project defined by selected regions, select the “Export cycle region only, or length of selected regions” checkbox.
For other ways to share from Garageband, checkout their online documentation.