I have a game in Unity app, it's a $3$D game where a character goes through some obstacles to save his friend, I've finished making her walk, jump and collect keys only, now I want$$ to complete several points in it$,$ which are:

$1-$ If the character falls three times, he dies completely and the game ends and the value over screen appears.

$2-$ I want to add sounds when collecting keys and coins.

$3-$ I want to display the number of remaining lives on the screen or for there to be a health bar.

$4-$ I want to complete the game appropriately and complete the deficiencies in it and in the user screen.

$5-$I want a nice ending where she saves her kidnapped friend by opening a door with the keys she collected or something like that but I don't know how to end it