What does IONISATION really mean?

For example. In a cloud chamber, when an ionising radiation passes through the vessel, the alcohol condenses on the trail left by the particle. What does this physically mean? Does the incoming particle (say, a muon) knock off an electron thus forming an ion? Shouldn't the muon be deviated then? And what if the incoming particle were an electron itself??

This question arises while I was studying how a silicon detector works: apparently it's the same principle, but I don't get how the incoming radiation (alpha particle, beta particles) can actually cause the creation of ions without its path being deflected...