Clean the steel tubing to remove all traces of grease, grim, dirt and oxidation.
Fit the steel tubing together as you want it. Secure the tubing with binding wire, a clamp or another tool so that it will stay in place if gravity alone will not hold the steel tubing.
Paint the tubing with flux where the steel tubing will be joined.
Heat the tubing with your torch. When the tubing is hot, put the end of your brazing wire at the join of your tubing. Continue to heat the joint of tubing with your torch while you feed brazing wire into the join. The brazing wire will melt and the melted wire will follow the flame and seal the seam of the steel tubing.
Check your work. Allow the steel tubing to cool to room temperature once the tubing is completely brazed together.