There are a lot of on-line tutorials. Here's a selection:
The basic step with Anne and Pablo of Tango Space. They have a great playlist of beginner videos.
The "walk" is the foundation of your tango. Neither its importance nor subtlety can be overstated; many dancers spend years learning, developing and refining their walk. Anne and Pablo of Tango Space have a great playlist on the tango walk, including: 3 key elements and walking in close embrace.
Five fundamental steps with Anne and Pablo of Tango Space.
Ten steps for intermediate dancers with Anne and Pablo of Tango Space.
Five common milonga steps with Anne and Pablo of Tango Space.