You can use several free audio jukeboxes to rip CDs into MP3s, but two of the most popular ones are Windows Media Player (WMP) and Apple iTunes.
For WMP:
For iTunes (on a Mac)
Both programs work equally well and allow you to select a bit rate of up to 320Kbps. If you want to take up less space on your hard drive, opt for a lower bit rate; use a higher bit rate if sound quality is more important to you.