By default the wallpaper picture is normally displayed once, in the position selected. You can have your pictures tiled over the desktop instead. Turn on tiling by choosing Tile small pictures and set the picture size that will trigger the tiling process. For example, if you set the height to 500 and the width to 400 any image that is less then or equal to 500 pixels in height OR 400 pixels in width will be tiled. Note that this tiling setting will override Best fit mode: i.e. if switched on then small images will be tiled rather than resized.
Always tile will tile all pictures irrespective of their size. In Best fit mode the image will be resized and then tiled.
In Windows tiling is normally done by placing the first image in the top left corner of the screen and tiling from there. In AWC you have more control as the position settings you select will still be used. So, if you have selected the position Right, the first tile will be centred on the right hand edge and the other tiles placed accordingly.
When checked the tiling process causes adjacent tiles to be mirror images of each other. If the Balanced checkbox is also set then the positioning of the mirrored tiles is adjusted so that they are balanced around the intersection point of the reflected images. Kind of hard to describe but play with it and you'll get the idea.
Click here for examples