On the starter screen of Visio you can choose a style of process map to create and the appropriate units to display (US or metric). Alternatively, you can select a style by using the New option under the File menu.

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On the left side of the new blank page you will see areas where you can select arrows and backgrounds. Another area provides access to a variety of basic flowchart shapes such as process steps, decision points, documents, data and storage, terminators and on- and off-page references.
Simply click on the symbol you want to add and drag it to the page where you want to place it. To have a new shape auto-connect to an existing shape, drag a new shape adjacent to the existing shape on the side you want to connect it to. You will see that the arrow on that side becomes highlighted. Let go and it will be connected with a standard connector.
Label each step simply by clicking on the shape you've added and typing the text you want to use as the label. Note that if the font size is quite small as you view it, the program will automatically zoom as you type. You can adjust this setting in the Options area of the Tools menu or increase the size of the page on your screen using the percentage control in the toolbar.
Continue adding process steps, decision points and terminators until your process map is complete.