Lines are used to divide space, direct the eye, and create forms. At the most basic level, straight lines are found in layouts to separate content, such as in magazine, newspaper, and website designs. This can of course go much further, with curved, dotted, and zigzag lines used as the defining elements on a page and as the basis for illustrations and graphics. Often, lines will be implied, meaning other elements of design will follow the path of line, such as type on a curve.
Lines also form the grid system, the basis for layout in design. Often these lines will be invisible, but they will nonetheless direct the flow of content on a page.
Almost any graphics software can be used to create literal lines. Adobe Illustrator is one of the most popular applications for creating complex shapes based on lines, through the use of the pen tool. Software such as Photoshop, Corel Draw and others can be just as effective.