how I show the error using PHP ?

I did the online rank tutorial using this tutorial construct.net/en/tutorials/creating-own-leaderboard-1032 however it is old and probably the owner of the tutorial already forgot about it and I have some doubts regarding PHP follows the doubts below

how do I show example: Your Position In Rank: 99

how do I show an error if the player puts a name that has already registered in the database?

The Tutorial only fetches the Top Ten Scores from the database.

You need to change the DESC LIMIT 10 in the Getscores.php file to whatever number you want.