There is no difference for the first flight. Introductory is just that one flight and a flight school with multiple lessons has flight one and beyond. I’ve done both for gliders flight lessons.
Many flight schools will offer a free or greatly reduced price intro lesson as a way for someone to see if they want to buy a flight school package. The introductory lesson will take a prospective student up in a small plane, something like a Cessna two seater, and actually let the “student”
try the controls.
An actual school package includes classroom lessons and also flight time.