Debut
I think it is the term some eastern European countries use to mean what we call an Opening.
There is no "best", just what works for you. If you can read English (I am not sure from your nationality but you posted in English so I am guessing you can) and can buy something comprehensive like the Mammoth Book of Chess, the recipe is to have a look at the wide variety of openings and ask yourself, "which of these leads to a middlegame in which I feel comfortable and good moves come naturally to me?". Do not be seduced by people pushing their "pet opening" because of a trap. You will never excel at chess by playing for cheapos.