Hey San,
I think you might be confused as to how playerprefs work. They can only be and int, float or string value and each playerpref has a key used to identify it. The key itself is always a string and you can call it whatever you like.
So if your game has 5 levels and you want to save a high score for each level you would need to create a playerpref key for each of the 5 levels like this:
Level 1 = highScoreLevel_1
Level 2 = highScoreLevel_2
etc...
When you create a game and distribute it, say you make a game for iOS and release it on the app store, when someone downloads and plays the games there will be no playerprefs installed with the game. You will need to create each playerpref either when the game is first run or when the player enters the level. That's when you want to use the "PlayerPrefs Set Int" action. The best way to do this is with the "PlayerPrefs Has Key" action.
So the first time your game is run you check to see if there is the highScoreLevel_1 key in your playerprefs. If yes then you want to get the value and load it into an FSM int value called something like "highScore". If no then you want to use the PlayerPrefs Set Int action to create it.
When the player dies you want to compare the players score against the highScoreLevel_1 value. If their score is lower then do nothing, if it's higher you want to overwrite the high score with the score the player just achieved.
So, in short, you only need to get the high score playerprefs value when you first enter the level, then you save the players score ONLY if it is higher than the high score stored in playerprefs.
Does that make sense?
Cheers,
Simon