1.INSTALLATION:

For installing it just install the zip file. Then the add-on will appear on the sidebar of the viewport (press N)

2.ADD DIRT:

Select the object that you want to add dirt. Then select the image that you want to use and click on add dirt. This will bring you to edit mode, now you can just create the bounding box where the dirt will be placed. This in general works better in surfaces with low curvature. You willl add the dirt only in the active material of your object.

IMAGE OF BOUNDING BOX, IMAGE OF DIRT ADDED

3.PARAMETERS OF DIRTY:

Once the dirt texture is added, you can edit.

• Blend: blending of the  dirt with the original texture, because this is a world space parameter, depending on the sacle of your scene you might need to play around with low parameters. IMAGE BLEND
  
• Noise Scale/Noise Detail: changes the parameters of the multiplicative noise that is used to blend the dirt with the original texture.
• Factor: amount of noise IMAGE FACTOR
  
• Roughness: the roughness of the dirt
• Image Scale/Location/Rotation

4. EDIT DIRTY:

• Edit: you can rearrange the bounding box of the dirt that determines the location of the dirt
• Delete: delete the dirt layer
  
• View: local view of the dirt layer
  
• Show Guide: Show guide of the bounding box

5. REFRESH:

Refresh the data from the blender file, this can be helpful to delete spare parameters or objects.