Neville's algorithm is like a helper to find the value of a function (like 2x + 3) when you only have a few points (like when x=1, y=5 and when x=2, y=7).
Imagine you have a ladder that goes from the ground all the way up to the clouds. You want to find out how high up in the clouds you'll end up if you climb up 5 steps. But you only know how high up you are after climbing 1 step (let's say you're 2 feet off the ground) and how high up you are after climbing 2 steps (let's say you're 4 feet off the ground).
Neville's algorithm helps you figure out how high up you'll be after climbing 5 steps. It does this by looking at the points you already have and making an educated guess on what the function might be. It then uses a special formula to work backwards from the points you have to find the height you'll be after climbing up 5 steps.
So basically, Neville's algorithm is a helpful tool for finding missing information about a function.