I have used "Ideal 720" rods for years,which are exactly the same thing,but a bit cheaper,and available in most welding supply shops.
Like Dale mentions,keep a stainless steel brush solely for this stuff.The area to be "welded" must be clean,and I also use a piece of 1/16 stainless rod to scratch through the weld puddle.This is required to remove oxygen from the area to be joined.
Heat the join indirectly,and scratch the Ideal rod on the join,until it flows.
Then scratch through the puddle with the stainless rod.When you can feel the base metal start to go soft,you're at the correct temperature.Try to make a neat job,because it clogs grinding wheels like you won't believe.
Practice makes perfect.I used to make my own mufflers for model RC airplane engines.