Illustrator is a great program for creating illustrations. However, if you want to blur background in your illustrations, there are a few things you need to know. First, make sure that your foreground and background are set up correctly in your drawing tools. This will help you create smooth and consistent illustrations. Next, use the Blur tool to blur the background in your illustration. The settings for the Blur tool can be found under the Tools menu in Illustrator. Be sure to use a low or medium value when using the Blur tool to blur the background. Finally, be sure that you have properly aligned your foreground and background elements in your illustration. This will help make sure that all of your elements are looking correct when viewed onscreen.