Photos or a video clip
Choose Photos to build a GIF from pictures you already have: a product from every angle, a before and after, a short slideshow. Drag them into order and give any frame its own time, so a title can stay on screen longer. Choose Video clip to turn a moment from a recording into a GIF; pick the start and end and how smooth it should be. There is also a quick video to GIF page if you only ever start from video.
Keeping the file small
GIFs grow with every frame and every pixel, so the size estimate updates as you change settings. The biggest savings come from a smaller width, fewer frames per second and fewer colours. Pictures with large flat areas compress far better than photos full of fine detail. Many chat apps limit GIFs to a few megabytes, and email attachments are often capped at 20 to 25 MB.
Colours and dithering
A GIF frame can only hold 256 colours. Each frame gets its own palette built from its pixels, which keeps photos looking natural. Smooth dithering scatters the remaining error between neighbouring pixels to hide banding; Pattern uses a fine regular grid that compresses a little better; Off gives clean flat colours, which suits logos, charts and screenshots.