Drop an .hdr or .exr file on the script and it will automatically create a VRay Dome Light. If a VRay Dome Light already exists in your scene, it will replace the HDR map. You can display it in your viewport in 1 click, then you will have simple main parameters as horizontal orientation and overall and render Multipliers. The separate Light & Background button allows to create a second Dome Light, to set lighting and visual brigthness separately.