Before I begin, I would like to point you to the Blender tutorials already avaliable. I'm only writing these because I was asked to and I'm going to go over Oblivion-specific examples. You will not become an amazing modeler from these tutorials. I'm only going to show how to do very basic things to meshes on your own.

Blender 3D: Noob to Pro: http://en.wikibooks.org/wiki/Blender_3D:_Noob_to_Pro
- Probably your best source for learning Blender from the ground up

Here is a list of all the hotkeys: http://en.wikibooks.org/wiki/Blender_3D:_Noob_to_Pro/Hot_Keys
- You'll need to learn many of these eventually if you want to become a more advanced mesh-maker, but I will mention all required hot keys when they are relevant.

On to the Lessons!

Lesson One: Introduction and Default Settings

Lesson Two: The Joy of NIF and The ol' Hack'n'Slash