PNG: useful for transparency and crisp graphics
PNG uses lossless compression and supports transparency. It is a strong fit for screenshots, diagrams, interface graphics and images where sharp edges matter. Photographs stored as PNG can become unnecessarily large.
JPG: a practical format for photographs
JPG uses lossy compression and is widely supported. It can make photographic images much smaller, but repeated editing and compression can introduce visible artefacts. JPG does not provide the alpha transparency commonly expected from PNG or WebP.
WebP: built with the web in mind
WebP supports both lossy and lossless compression as well as transparency. For modern web projects it can often reduce transfer size while keeping useful image features, although your workflow or target software may still require PNG or JPG.
A practical rule of thumb
Use PNG for lossless detail or transparency, JPG for photographs that need broad compatibility, and WebP for web images. Check the output because changing formats does not guarantee a smaller file.