To open an existing animation:
The Recent Files sub menu located in the File menu provides quick access to previously opened or saved animations. You can configure the number of recent files from the options dialog.
You can select any supported image format, if it is not a GIF file, then a new untitled animation will be created containing the selected image as the first frame.
You can also drag and drop images from File Explorer and other applications onto the Gif Animator window to add them to the current animation.