Sort-of memes that are cracking you up at the moment

PNGs are generally best for all-rounders or if you don't know what to use.

GIFs are best for computer generated graphics... block colours, fonts, etc

JPGs are best for photographs

BMPs aren't good for much, unless you need to paste into a Microsoft Word document

TIFFs are best for really high quality photographs that aren't RAW

RAW is best for the equivalent of a digital negative, where you can still adjust light and colours

Those are the base file types, things like PSD files are then containers for those with effects, layers, masking, etc.

If in doubt about what to put online, use PNG, if it's a photo use JPG, and for everything else there's GIF

Hate to be late to the party but BMP's are good for creating textures/layers in Indesign when Vectors are too clean and large in file size, YES, large in file size...

GIFs are good for being awesome.