Article: SmartArt creates a new graphic layout for you to add data. It does not transform your existing data, so create a new blank spreadsheet for your timeline. Depending on your version of Excel, either click the SmartArt tab in the ribbon menu, or click the Insert tab, then the SmartArt button. This option is available in Excel 2007 or later. Click Process in the SmartArt ribbon menu, in the Insert Smart Art Graphic group. In the drop-down menu that appears, select Basic Timeline (a right-facing arrow). You can adapt various other Process graphics to use as timeline. To see the name of each graphic, move your cursor over the icon and wait until the hover text appears. By default you only start out with a few events. To add more, select the timeline. A Text Pane should appear to the left of the graphic. Click the + button at the top of the text pane to add a new timeline event. To enlarge the timeline without adding new events, click the timeline to show a box outline. Drag the right or left side of the box outward. Type in the Text Pane box to add entries. You can also copy-paste data into the timeline and have Excel guess at how to arrange it. Typically, you'll end up with each column of data as a single timeline entry.

What is a summary?
Create a new spreadsheet. Open the SmartArt menu. Select the timeline from the Process submenu. Add more events. Edit your timeline.