Lol. Is it hard to google?
And well, I havent coded chess programs but I would guess it is more like a extensive and brute force program.
And the score is reliable but you need to know how to interpret it.
That number shows how much centi pawns one side is up. In that case Black which I would guess was the computer was .59 centi pawns ahead. That means he has a clear edge but it is not winning yet.
You can read on google as I said tho, I wont write millions of chess posts and web pages for you on this post when you can easily find them on google.
https://www.chess.com/article/view/chess-engines-evaluations
This generation is going to hell, in my times people looked on Enciclopedias before asking to a bunch of unknown internet users.
What can be said about score number? What it measure? Is there very complicated algorithm that measure the situation on board? How realiable is that score level?