If you've just bought a Mac but don't know how to get started, here is a very quick guide to essential settings for ripping CDs and changing the system audio output.
Setting up iTunes for CD ripping:
Open up iTunes. Go into the Preferences (in the iTunes menu). In the Import Settings you want to select either Apple Lossless Encoder or AIFF (the former has smaller file sizes but no loss of music data) and, most importantly, check the box for error correction.
Connecting your DAC:
As for connecting your DAC, you can use USB if available or you can use a Toslink to mini-optical cable from the headphone port of the MacBook Pro, iMac, Mac Mini or Mac Pro.
Selecting audio output and sampling rate:
If you are using optical, it will already be set to use optical as the output by default when a mini-Toslink cable is plugged in. For selecting the sound output with USB devices, double-click on your hard disk icon, then on Applications and inside that Utilities. Open up Audio Midi Set-Up and select that as the audio output. For switching around outputs quickly, I recommend using SoundSource, which adds a system-wide menu allowing you to quickly select the audio input and output.