While listening to the tracks are the best way to judge the quality for yourself, you should be aware of the implications of parameters like the sampling rate, sample size and overall bit rate. There are some standard sampling rates that are used such as 22 kHz, 44.1 kHz, etc. Usually the higher sampling rate will yield better audio quality. Sampling rate beyond 44.1 kHz usually does not exist. It does not improve the quality audibly either beyond the 44.1 sampling rate. Sample size in bits usually is 8 or 16. Once again 16 bit samples gives you better quality. As sample rate increases and you choose bigger sample sizes, overall bit rate increases. There is a trade off involved. Higher bit rate gives you better quality but it also causes a larger music file and consequently a larger presentation. So if you are thinking of distributing it electronically you should watch out for the overall size. Usually smaller sized files are easier to send and publish on the web. WAV files have similar considerations. The MP3 files are generally smaller as the format compresses the original audio to produce smaller files.
For your own protection have your defenses up totally. Have the firewall up and the ant-virus active. That will protect you from malicious content being downloaded to your machine. Once you have your guards up, there are plenty of resources in a truly wide-ranging selection available for you. The best thing to do is to get started with the free stuff and once you get experienced at using the sound files, graduate to better audio files that may not be free, but will usually be of superior quality.