Start with the old long-term release version, QGIS 2.18. There are many free tutorials and resources for this version. There's a list available here: Seeking QGIS tutorials and web resources?
The current long-term release version (3.4) came out very recently, so there aren't as many tutorials available. Upgrade to 3.4 once you feel comfortable with the basic functions of QGIS.
Minor versions of QGIS come out every few months, but stick to the long-term release versions because the new versions are always buggy. When you're just learning it's very hard to tell the difference between a bug and user error.