would just be a txt file. game loads you read in a score.txt file ( file you make in your game folder) to an array as the plaeyr plays the high score array is updated to reflect new/repalced scores.
when player picks option to quit/exit game. just write the highscore array back to the score.txt file
so, just look up basics of how to open, read from, write to, and close a file
manual covers the instructions well and im sure George has covered reading and writting variable data from/to a text file several times before (AUMs and georges scripting tutorial?)