A GIF file is an image file format that can contain one single image or multiple images. When it contains multiple images, it looks ‘animated’. An animated GIF file thus needs to have 2 or more sequential images, each to be displayed for a specific interval of time.
While you can always use advanced photo editing tools like Photoshop, GIMP, etc, using some free GIF animation freeware make the job very easy.
GIF animator freeware
GIF animator freeware
