Pick a size before you start
Square 1080 × 1080 and portrait 1080 × 1350 are the standard post sizes for most social feeds, story 1080 × 1920 fills a phone screen, and landscape 1920 × 1080 suits banners, slides and video thumbnails. Changing the size keeps your photos and layout, so you can make a version for each place you share.
Framing each photo
Every photo fills its frame and is centred to begin with. Drag it to choose which part shows, for example to keep a face in view in a narrow strip. Grids with more frames than photos leave the extra frames as background, and the fit-all layout always makes room for exactly the photos you added.
PNG or JPG?
PNG keeps every pixel exact and is the better choice when your collage has text, graphics or a plain background. JPG files are much smaller and fine for photos, which helps when an app limits upload size.