There are TONS of tutorials on Zbrush. The tool itself is not free- it's $800 now, I Think... BUT... it has more tools than most people will ever need. They have a smaller version that you can use just fine for just about anything, and that costs way less- Zbrush Core. Same company also has a cool tool that they do give away for free: Sculptris. https://pixologic.com/sculptris/

Another very powerful sculpting tool that is free is Blender. Also has a ton of tutorials / community.