Not easy to answer in great detail.
In General checkmate is a winning position as are the positions from the moves leading up to that happening.
Any position the opponent resigns in is a winning position.
That usually agrees with your feeling you have a won position but sometimes opponents see ghosts and resign anyway. A 'good' position that confuses the opponent would seem to be a winning position if it makes them resign or even just blunder away material.
A complex but unclear position with the opponent having little time on his clock may pressure them to either resign or to blunder and then resign. Or they may lose on time anyway when the flag falls [or these days the red light comes on]. So a position where the opponent can not make his moves before the flag drops is a winning position even though without any time limit it might be lost.
In general with sufficient material advantage the win should be a matter of technique. So any position that allows for a combination to win material could be a winning position and usually is but not always. Clearly sacrifices are often made to get a winning attack so in such cases material is irrelevant.
Leading up to those types of positions are less clear positions that are merely one with an 'advantage' not yet winning. More space, better piece positions, time advantage both useful moves ahead or on the clock, or 'initiative' are more likely to lead to winning positions and then to won positions and finally a win. These factors are subject to surprise tactics as well as not being followed up properly so as to continue building the advantage until it is overwhelmingly a win. So while good, they are not yet properly called winning.
To summarize, a winning position depends on many factors, but whether it is called winning or not depends on the judgement of the person evaluating the position. And sometimes those persons are wrong. Also each player has a different spot in the gray area where they would call it winning instead of just having an advantage.