Jerry, open your RGB image (preferable at a linear stage), run the script, select your Ha and your RGB image in the corresponding fields, put the sliders regarding Ha and RGB bandwith (7 and 100 are for Baader filters), and play with the three buttons (Show Ha, Show RGB, show HaRGB) until you are happy with the settings. Zoom in-out the preview image. I usually skip the color calibration/SCRN to green, etc, I'm doing them later manually.
Mind that the script is made for HaRGB, not HaLRGB. HaLRGB is a bit....tricky? How you put Ha in L without killing the other colors? My only attempt ever on this was to join with pixelmath L+Ha (Ha in a small percentage) and then use this as a new L for an already HaRGB image.
I hope I help a bit