For a Video Tutorial on this process see:
Video Tutorial ~ Select Image or Slideshow for Main Page

For a rotating slideshow of images, see this FAQ:
How to Set Up a Slide Show on your Home Page

The size of your main page image is controlled by your template choice.
See this FAQ:
Main Page Image, Thumbnail Image & Zoom Image Sizes per Template

To display multiple still images on your Main Page, you will need to add images into the Main Page Text field. See this FAQ:
Add Image to Text Editing Screen

Choose the image you want to show on your Home Page

• login to your FASO account control panel
• click Your Site's Home Page  (left column)

• for Main Page Picture, find your image visually by clicking Choose an Image (screenshot #1) 
  or clicking Change Image  (screenshot #2)
• You can also click on the up and down Arrows icon to select image by title
  

screenshot #1

screenshot #2

• choose an image to select it or click on Upload New Image

• Click on Save Changes when complete

Add a Composite, a Photomontage

It can be very effective to create a photomontage (multiple pictures put together as one image) and select that image as your Main Page image.

1. create the photomontage in your image editing software, like Photoshop or Photoelements

2. upload the image to your Images folder
(see FAQ: How do I upload and edit non-art images?)

3. select image as your Main Page image.
(see above)

Example:

07022019