Instead of clicking save, click export. Export then change it to the name you want with *.png* but also save it as xcf file which only can be opened with GIMP so if you want to do any further changes to your poster, you still have it in layers. Hope this helps. :) -Color4gimp tutorial

You have to export it not save it ^.^

I don't understand. To make it in image like png, gif gotta to click export

You go to export to then select a file to put it in then change the name to whatever you want...the you press export then press enter and DONE