Javascript: Buttons, Texts and Fields

[Liv.u]

Hi, Im not well versed in javascript. Im a total beginner and im struggling immensely to add buttons/Scripts that do each of the following:

• Add text AND Text fields
• Hide/show text and Text fields 
•  Remove text And Text fields
• Totaling and adding percentages
• Setting a limit to Percentage totals
• Error messages 

I want to recreate these functions. I added a video to clarify. 

https://clipchamp.com/watch/mseL30lBUpp