I have already added a score in my project but I want to have a high score in it
can u help me?

You can just use a global variable and compare the current score to the global/high score. If current score is > global/high score then we have a new high score and Do = currentScore to HighScore. If you want to save it, you can use the storage actions to save and load. If you want to save it online you are going to need PHP and MySQL and a web server.