Installation
Drag and drop the downloaded ZIP file directly into the Blender viewport, then confirm the installation.
Alternatively:
Go to Edit → Preferences → Add-ons
Open the top-right menu and select Install from Disk
Choose the AP_MeshExtender ZIP file and confirm
Enable AP | Mesh Extender if necessary

Preferences

Open Edit → Preferences → Add-ons and expand AP | Mesh Extender.

Show in N-panel - Shows or hides the Mesh Extender tab in the 3D Viewport sidebar.

Hotkey - Customize the activation shortcut. The default shortcut is Ctrl + Alt + E. 

Workflow

Select a mesh object
Open the Mesh Extender tab and click Extend, or press the configured hotkey
Drag a handle with the Left Mouse Button to extend the mesh
Drag the same handle with the Right Mouse Button to add or remove edge loops
Press W to toggle the wireframe overlay
Adjust multiple axes if needed
Press Space to confirm or Esc to cancel