Depending on the version of Microsoft Office you are running, you are going to go about things a little differently. When you first click on the program icon and it begins to load, a splash screen will briefly appear. It will tell you if you're running Office 95, 98, XP, 2007 or Vista. If this screen disappears too fast for you to tell, you could always check the documentation that came with the software when you purchased it.
In the 2007 version of Microsoft Office, select the "Insert" tab from the main row of tabs near the top of the program. Then select either the "Smart Chart" or "Chart" options, both of which will allow you to enter information that will go into your flow chart when it is added to your document. In older versions of Office, select "Chart" from the "Insert" drop-down menu, which will then allow you to enter in your data as necessary.
Once you have selected the "Chart" option, customize it before you even begin to enter any data. Select the type of flow chart: you can display your chart using columns, lines or bars. You can also change the colors of the chart to make it easier to read as well as make it more aesthetically pleasing. Create your flow chart completely from scratch, or use one of dozens of pre-installed templates or find hundreds more templates on Office Online (see Resources below).