With this jig, you can only make finger joint with the thickness of your saw blade. In my case 3 mm. You need to have a strip aluminum or some scrap wood with the same thickness.
And you also need a table saw sled (for example this one http://woodgears.ca/delta_saw/small_sled.html)
The most tricky part is how to make the first cut and how to make sure that your joint is well aligned. I put the first piece flush with the aluminum strip. The first cut of the other piece needs to shift with the thickness of the saw blade.
You don’t have to saw one at the time. In the picture below I made 4 joints in one go.