Hi,
There’s a thread about what happens when things go wrong (using iTunes & Picard) here.
Common advice for new users includes:
- work on small batches of files at a time. Picard can get bogged down if you feed it too many files at once.
- work on a copy of your files (as @aerozol said).
- experiment first to make sure that you’re getting the results you want. If not, tweak the settings in
Options → Options → File naming
andOptions → Options → Advanced → Scripting
as needed. The docs cover the basics, and the forums are a great place to ask more detailed questions.