This could be clearer. The individual mandate is a mandate to get insurance, with some people exempted. If one does not, a penalty applies, with some exempted; but the penalty is the only consequence imposed for not having insurance.
The Supreme Court did not label the individual mandate itself as being a tax. It upheld a use of the power to tax as a way to impose the penalty. Tax law has many provisions to spur or deter conduct. The court found that the penalty is of that nature: It discourages forgoing insurance.
The penalty itself does not even apply to anybody having insurance. It will likely affect only a tiny percentage of people, as it succeeds in spurring what the individual mandate actually does mean: Get health insurance.