M4A could mean AAC, which is similar to MP3, or it could mean Apple Lossless (ALAC), which is similar to FLAC. The easiest way to find out which one:
In iTunes, view your music library.
In the iTunes menu bar, click on View -> View Options…
In the pop-up menu, check "Kind" and click OK.
Now, in the kind column, iTunes will tell whether an M4A file is AAC or Apple Lossless. (You may need to scroll to the right to see the contents of the column.)
iTunes is fine for importing music from CD's. If you want to import in the ALAC format, you will need to specify that in the iTunes preferences. I also recommend using error correction when importing CD's.
For the truly paranoid, a free application called XLD (aka X Lossless Decoder) can be used to rip CDs and verify the ripped files with the AccurateRip database. It will ensure that the rips are perfect, but in practice, this is not typically an issue when ripping with iTunes. XLD is also an excellent application to quickly and easily convert FLAC files to ALAC (actually it will convert to and from many lossless and lossy filetypes).