Buddha is used mostly to refer to someone who has been enlightened and has, therefore, attained a spiritual height to be called a divine being. Such an individual has mental activities under his control. And his mind has been reformed that he can effortlessly uncover the truth behind certain situations of life.
A Buddha is also a sentient being that has been transformed to the point that he can see the reality of things in their real nature. All these are being done with a very calm, peaceful mind. On the other hand, Bodhisattva is a combination of two words, i.e., Bodhi and Sattva. Bodhi refers to knowledge or wisdom in its purest form.
Sattva refers to the nature of mind, which is characterized by peace, calmness. Bodhisattva is a word that describes an individual that is currently in the process of becoming a Buddha. So to achieve this, such an individual needs to pursue bodhi and sattva so as to become an enlightened being.