Anne
Artwork usually refers to the images and backgrounds used. If you need to create the artwork for a poster and leaflet, normally you would use an application that allows you to draw or edit images. Professionals use Corel Draw, Adobe Illustrator, Corel PhotoPaint, Adobe Photoshop to create images to use as poster art. For you, try something like GIMP, which is a free image editor and works very well, or you could upload a photograph into an online editor like what is available on Picasa or Pixlr or Picnik. It is easiest to start with a photo if you are not a little bit trained in graphics because you will have the best chance of a good result, plus it is your photo, so there is no chance of copyright infringement. Once the image(s) are created, you could use a text editor to design the poster or leaflet, however, GIMP is good for layout as well. You would have to play around with it, but that's just what happens with any new applications. Learning curve!