I have to do an assignment in Processing using mainly classes and arrays. To be exact, I have to create a simple game.
I came up with a space invaders type of a game and I have already objects for the 'enemies' and the player and the missiles, but I don't know how to create a new instance of an object each time an argument is met and then when another argument is meant, I'd like that object instance to be destroyed.

Anyone knows how to go about this?

i assume you have some kind of list that keeps track of active ones so that it can be drawn. to create a new one, use the 'new' keyword to create the object, then add to the list. to 'destroy' your object, simply remove it from the list.
https://processing.org/tutorials/objects/

What do you mean by the list?



here's what I have currently ->

have you not gone over data structures yet?


Like, arrays for example?

An array can be thought of as a list

ok, so you already know how to create new players and missiles since i see that in your setup. your real question is "how can i use a collection to maintain more than one missile?" and the answer is to use an arraylist:

https://processing.org/reference/ArrayList.html

create an array list, and use a loop to create however many missiles you want and add them to the arraylist. in your draw method, you loop through your arraylist and draw everything in it