Short answer
Subclass 189 and subclass 190 are permanent skilled visas. Subclass 189 is generally an independent skilled pathway, while subclass 190 requires nomination by an Australian state or territory government.
Both visa subclasses are part of skilled migration and use SkillSelect-style requirements such as invitation, occupation, skills, English and points-test criteria.
The practical difference is the nomination pathway. Subclass 189 is not based on state or territory nomination in the same way as subclass 190. Subclass 190 requires the applicant to be nominated by a state or territory government agency.