OPEN DATA opens a datafile,loads it into ViSta, and displays it as a datasheet.  It is the first step in a data analysis.  

When you use OPEN DATA, ViSta will then open a file dialog, which you use in the usual way to find your data.

After you open your data you will see a datasheet of your data.  You may use this datasheet to browse through your data. EDIT DATA lets you edit it. 

When you are finished with the datasheet you should close it. You will then see that other ViSta windows have changed: The WorkMap will have a new Data Icon.  The name of the Data Icon will correspond to the name of your data.

If you are using guidemaps, you are now ready to open your data. After you open your data the OPEN YOUR DATA guidemap will be replaced by the DATA ANALYSIS guidemap.  Click on the !! side of the OPEN DATA button and use the file dialog to find your data. 
