There are a variety of ways to populate your carousel.
Images attached to the current post
Upload images to your post/page and use the shortcode [[wp-flowplus]]. The photo title will be displayed below each image. The image may link to either the large size image in a Lightbox or to a link that opens in a window.
Images attached to another post
Images uploaded to another post/page may be specified using the shortcode [[wp-flowplus id=post_id]]. The photo title will be displayed below each image. The image may link to either the large size image in a Lightbox or to a link that opens in a window.
Images from a folder
Upload your pictures to a folder and use the shortcode with dir argument [[wp-flowplus dir=FOLDERNAME]]. The image name will be displayed below each image and all images link to the Lightbox. The folder path must be configured in the WP Flow Plus settings.
Images tagged in the media library
Tag images in your media library using the Media Tags plugin by Paul Menard and use the shortcode [[wp-flowplus mediatag=tagslug]]. The photo title will be displayed below each image. The image may link to either the large size image in a Lightbox or to a link that opens in a window.
Images listed by ID from the media library
Images in the media library may be specified by ID using the shortcode [[wp-flowplus include='1,2,3']]. The photo title will be displayed below each image. The image may link to either the large size image in a Lightbox or to a link that opens in a window. To force the images to appear in the order listed, use the option orderby="post__in".
NextGen Gallery
Create a NextGen gallery and use the shortcode [[wp-flowplus nggid=1]] where the number corresponds to your NextGen gallery ID. The NextGen thumbnails will be used in the carousel. They will link to the large size images in the Lightbox. If your thumbnails are blurry, try regenerating them in a larger size.
Featured Posts
Create a featured posts gallery by using the shortcode [[wp-flowplus category=slug]]. The carousel will display each post's featured image, and will link to the post.