1. Install:

Open Edit-Preference-Addons and press Install button, locate the downloaded zip file and install it, you should get a marmolight tab:

here you can define addon tab name (default it ML, restart blender to take effect) and change hotkeys.

2. Load HDRI

addon panel is located on the right side of 3d viewport. you can load selected HDRI image into scene. open the image folder and add your own image. hdr, exr, jpg, png, tiff type are supported. after copy paste your own, press refresh button to update the preview images. you can find free HDRI images on sites like hdri haven.

use intensity slider to dim the HDRI

3. Add Lights from HDRI

you can add lights from HDRI image, which keep the relevant light source direction and color. use LMB to add light under mouse cursor, Z to remove last light, ESC/ RMB to cancel, Spacebar or Enter to confirm.

4. Pan Around the Scene

hold  Shift + RMB and move left or right to pan the lights as well as HDRI around.

5. Add Light from Current View

you can add custom light with set default color and strength from current 3d view. please note it is stationary.

6. Add Camera from Current View

you can also add camera from current 3d view, use Lock Cam to move the camera around for best shoot angle. if the active object is camera, it will go to its view, if it is any other type of object, it will create new camera at current 3d view.

7. Add Backdrop, Stand

it is simple to model a backdrop/stand, but it is easier to press a button.

8. Realign Light, Increase/Decrease Light Strength

under MISC tab, there are three more operators that are intended to be used with hotkeys. you can change the hotkeys at addon preference.

Realign Light: make active light point toward mouse cursor.

Increase/Decrease Light Strength: increase or decrease the light strength from selected objects. easier to fine tune the result after add lights into scene.