Generally, a guitar connection to a Mac looks like this:
Let’s see how it’s done in detail.
Note: we suggest to use guitar adapters or external audio cards that use a USB port for connection—they provide a much better sound quality and almost zero feedback comparing to regular guitar adapters.
Use a connection guide that came with your device. Each device has its own connection scheme, but the general rule is to plug the device into a USB port or the headphone jack on your Mac.
If your adapter has a volume control, be sure it's not set to zero.
Use any guitar cable with 1/4" jack. For example, like this one:
Plug one end of the cable into your guitar, and the other end into the adapter or audio card.
Click the "Input settings" button on the preset page, then select your device in the list of Input devices.
That's it! Your guitar should be connected now, and you can start playing.
Decrease the volume on your Mac before choosing an input device due to possible feedback and noise.