how to add a formatting menu bar to Atom-“cut”, “copy”, “paste”

You can extend Atom’s feature-set by installing third-party packages. There might be a toolbar package, that already supports those action. Another option is to install flex-tool-bar and create a config file that adds your desired features.

Example:

[
  {
    type: "button"
    icon: "copy"
    iconset: "fa"
    callback: "core:copy"
    tooltip: "Copy"
  }
  {
    type: "button"
    icon: "cut"
    iconset: "fa"
    callback: "core:cut"
    tooltip: "Cut"
  }
  {
    type: "button"
    icon: "paste"
    iconset: "fa"
    callback: "core:paste"
    tooltip: "Paste"
  }
]