Hi a few questions.
Do a stars have lagrange points?
Well, you need two massive bodies in fairly close proximity to create such a point, so no, there is no such thing for a star, except in multiple star systems. The nearest objects are many stars at great distances, and the mass of the galaxy. Nothing could create such a semi stable point.
If a star has lagrange points then where would they be in our solar system?
See above, not applicable for our system, since it's an isolated star.
What does a star actually orbit in a galaxy? Even if its in the outer rim? Is it the cetural black hole?
The star orbits the center of mass of the entire galaxy, called the barycenter. Even the central black hole orbits the same point.
How does our sun interact with the stars around it?
Not much, except by exchange of electromagnetic radiation (light, radio, X-rays, etc). In effect, the interaction is near zero.
How many different stars can be in a star system?
Well, there's no definitive limit; the largest I know of is about 8, though a dedicated search might find a larger system.
How big is the biggest star?
You would have to phrase it the biggest star we know of, since there could be larger ones out there we haven't found yet. The largest I've found (masswise) is LBV 1806-20, which might have a mass more than 200 times that of the sun. Antares has a radius about 400 times that of the Sun, so is bigger in volume despite being smaller in mass. Any of that could have changed in the lest few weeks or months as we continue to explore.
Where in the galaxy did our sun come from?
No good answer to that. It formed from a cloud of gas and dust that was probably orbiting the galaxy in about the same orbit as the sun does. But since it has completed quite a few orbits (18-20 roughly) since it formed (as has all the surrounding material including nearby stars that formed around the same time, each on their own different orbit), you can't point to a particular spot and say "there". There isn't there anymore, it's somewhere else