What does it mean (for piano) when there are 4 sharp signs just after the treble clef?

the sharp/flat signs after either clef are your "key signature" for instance is there is a sharp sign pn the F line that means that every F will be sharp throughout the entire song, high or low, unless specified other wise.. if you come to an F in the song that is marked natural then you play every F in the measure as natural but then go back to sharp. It's the same for every note in the key signature.