The importance of Plotinus is not only his own philosophical ideas which are quite interesting, but his historical impact as the founder of neo-Platonism which is the main philosophical tradition of late antiquity.

For Plotinus, what really exists are the Platonic forms, so the true nature or form of things like justice, beauty, maybe numbers, things like that, and these he associates with the intellect because they're the objects of intellect, they are things that intellect can think about.

Assuming there is an intellect, we're clearly not this universal intellect or we would know it. So that's one function of soul.

Your soul existed before your birth, your soul will exist after your death.

Plotinus thought that the entire world has a single soul. He also thought that each animal and plant and of course human, has an individual soul.

The intellect must be different from the soul.

There's going to be this realm of Platonic forms and then there's going to be this single mind, the 'nous', which grasps them.