Walking is basic to most tango step patterns. This makes it easy to get started dancing right away, though there is surprising complexity behind this apparently simple activity. You will learn more about that in each lesson.
For now, start the music, close your eyes, and listen for each major beat. Then begin stepping in place to each major beat. When you feel natural moving to this rhythm, open your eyes and walk around the room, trying to step exactly on those major beats. Don't worry about anything else; just practice this SLOW SLOW rhythm for a few minutes. This rhythm is central to tango, though as you become more expert you'll learn how to spice up your dancing by varying this basic rhythm.
Now walk some more. This time, walk counter-clockwise around the outside edge of the floor. This is called the Line of Dance; it helps dancers avoid running into each other. (If other people make it impossible or dangerous to follow the LOD, you may briefly travel against it or even cross the empty center of the floor, then continue the LOD.) Place obstacles in your path to simulate people (or imagine them), then curve your walking to the left or right to go around them.