The most recent version of GarageBand requires MacOS 10.13.6 or later. The program occupies roughly one gigabyte of storage space. Previous versions of GarageBand are not available to download.
Many Apple products come with GarageBand pre-installed. If necessary, GarageBand is offered as a free download through the Apple App Store, or through Apple's website here:
Following installation, it is recommended to check the Audio Preferences within GarageBand. From the top menu, Preferences can be selected within the GarageBand menu, or by using the keyboard shortcut ( Command + , ).
If an audio interface is connected to the iMac, it can be selected from the drop down menu by choosing external speakers. Otherwise, select internal built-in speakers. For an iPad and iPhone, the built-in microphone and speakers are selected.
Need more details? See the video below.