How do I add a class selection screen?

I am working on a multiplayer HTML zombie horde survival coop game but before I start the complex mp part I want to work on the basics and now I have another question, How do I make a class selection screen?

Kind of like this:

Im super new into game making and stuff, so please be patient with me!

(Also how do I make the playable bounds infinite, I don't like the invisible walls, or at least make the playable bounds SUPER huge)

Here is a pic of the "code" I have so far:

To my understanding your class selection will be 1 dedicated layout where you have a background from your picture and you can put either the class sprites or invisible sprites for the player to select his class.

Then have some global variable which regulates which class is playing.

Upon pressing whichever button/sprite the player you set the global variable to that class + you send the player to whichever next layout such as level 1.

You then use, I hope, an invisible sprite for your player covered by the pinned player graphic. So depending on which class was selected you simply pin that graphic on your player.

uh, thanks.

You are welcome