I am doing some landscaping on my own and have very little knowledge
unfortunately.

A perennial: Does that mean it grows back year after year without
having to be re-seeded? That's what I would think.

Do these perennials spread automatically? That's what I would want
for groundcover and whatnot.

Thanks in advance.

I would ask these questions of a landscaper, but they won't return my
calls. Must be very busy.