Some things have changed over time with different Versions.
Product is the actual Product Name. This cannot be changed, but you may notice if you change Name, then the Product field will change too.
Namewas a method of changing the way the Menu Button displayed for the Product, before Header was even available
Header is the “new” method of changing the way the Menu Button displays for the Product and was added in a later version. It supports certain other syntax like <color>, <size> and <img> tags, which Name does not support.
For most purposes these days, you should only be changing the Header field and leave the other 2 fields as-is, untouched.
Press any of the category buttons to select (they all look the same at the moment as ive just copied the same one and renamed it into the different menu ready to add products to)