The article I read was: https://expertphotography.com/double-exposure-in-photoshop/
Here is what I learnt from reading this article.
EQUIPMENT
The equipment you need to create a double exposure photograph is - A camera and lens, Two different scenes, people or objects to photograph and editing software.
TAKING A SILHOUETTE PHOTO
One of the photos needs to be very dark or a silhouette. One way to create this type of photo is to use backlighting. This is where you have a bright light behind the subject that you are photographing. This does not have to be special lighting it could be an open doorway or window. Just remember that the sun should be behind your subject.
You need to try to underexpose the photograph so that it is dark. You can do this by setting the camera to manual mode and shooting or using the aperture setting and then using the negative exposure compensation value scale.
Ideally, you want as little distractions in the background of your subject as possible.
TAKING THE LANDSCAPE OR PATTERN PHOTO
You now need to take a photograph of something that you want to overlay with the silhouette. Things that work very well are patterns or landscape shots. There are two types of images that you can create, one where the silhouette makes an area darker and one where the double exposure seems to be on a white background.
Style 1
Source: https://expertphotography.com/
Style 2
Source: Matt Antonioli on Unsplash
If I you go for style 1 you can use the camera settings that best suit the thing you are photographing. If you want the white background then it is best to over expose the sky/background in your photo.
EDITING STAGE
Open each photo in the editing software you are using. In the silhouette photo, bring down the shadows and blacks to make the silhouette a really dark black. For the second image just make sure the exposure is how you want it to appear. This is also when you can adjust colour etc to match your final idea!
If you want to create a style 2 images then drag down the blacks and shadows, then pull up the whites and highlights so you get a completely white background. If there are any remaining colour patches paint these in so they are either black or white to match. For the second pattern/landscape image, drag up the whites and highlights to make the sky super white. Again paint in any areas that are left (flatten the image).
Use the healing tool to remove any distractions, specks, hair etc.
Now copy and past the one image over the over, so you are working in one document now with two layers. Make sure the silhouette is on top. In the layers options change the layer from 'normal'to 'screen'. This will now start to look like a double exposed image.
Now you just need to play about with the landscape/patterns layer size or placement to get the effect you want.
Lastly have look at various adjustments you can make to the patterns/landscape image, you could try exploring colour, lighting, black and white etc.
Source: Unsplash
Photographer: Abdalian, Leon H
Source: Unsplash
Photographer: Gift Habeshaw
Steps written out here...
Explain why you made the edits you did.
WWW: Are you happy with the outcome?
EBI: What could be improved?