With the release of GIMP 2.8, the ability to save the images in any type you want was removed. Yes, you cannot save your work as .jpg, .png, or .gif.
Instead, GIMP 2.8 introduced the capability to export your work to those types and saving defaults to save your work to GIMP’s native file, xcf.
It may be different to what you’re used to but GIMP’s move to add the export feature really organizes the UI and the flow of the ‘saving’ process which includes GIMP’s native file format or exporting to the image type that you want.
Export your image by going through File > Export or by shortcut key Shift + Ctrl + E.