New to using source code. How do I make this main menu idea?

[ClvrrCleaver]

Describe your problem here.

Me and my friend are making a mod and I decided to start trying to learn a bit of code for it and so far I've got something pretty good but I wanted to make it so that story mode is in the middle and the others aren't on screen so when you press up or down story mode will scroll up or down and the next option would come from the opposite side. I don't know how complex this is and honestly I don't even know where to begin so if anyone could help me with this I'd really appreciate it!
I attached some images to try to better describe what we want and what I've made so far.

Are you modding a build from source or with Lua?

Source

What is your build target?

Windows x64

Did you edit anything in this build? If so, mention or summarize your changes.

Yes, I replaced the menu and game over music and have edited the menu as what you can see in the attached image as well as adding my own week, songs and characters.

[baobab121]

change positions of buttons and move them with FlxTween

[ClvrrCleaver]

change positions of buttons and move them with FlxTween

how do I do that I still don't really understand most of this code