Conscience and conscious come from the same Latin word conscius and their word elements mean with and knowledge, but they are used differently.
conscience: (noun) sense of the quality of one’s character and conduct; adherence to moral principles; consideration of justice.
This is the “voice” in our heads that kicks in when we have a decision to make involving what might be morally right or wrong.
conscious: (adjective) aware or awake; involving thought.
A conscious person is aware of their surroundings, aware of what he or she is doing, and acting deliberately.
It can be used with a noun in a phrasal adjective, as in self-conscious, health conscious, or budget conscious, and refers to someone who is concerned or sensitive about their image, health, or finances, respectively. (antonym) unconscious
consciousness (noun) mental awareness
conscientious (adjective) scrupulous or careful. A conscientious objector is someone who objects to a requirement on religious grounds, such as vaccinations or serving in the military.