If you're not graphically or artistically minded it can be a real strain trying to create an attractive 'something' - be it a presentation, poster, Facebook cover, Facebook post and so on. The design interface is very simple - choose the type of image that you want to create, then look at the layouts available and choose one, find yourself an image from their extensive library (some images are free, others will cost you $1) or upload your own. Choose font, font size, backgrounds and so on, and then create your image. I've given you a screenshot below of the design stage.
You can then describe and hashtag your work for other people to find, or you can just download it there and then. It's a really nice, straightforward tool that, if you're struggling with design, or you simply want quick, smart professional looking images, is one to explore.