In Tableau, a Dimension (listed at the top of the Data window) is a categorical variable, including text variables, date variables, geographic location names, and discrete numerical variables. A Measure is a continuous numerical variable, which includes geographic coordinates.
Tableau expects a very particular structure for the data you import. In some programs this is called a "tall" or "narrow" format, rather than a "wide" format that is occasionally distributed by data producers. There are a variety of tools that can be used to reshape (or unpivot) data in this fashion, including the Tableau Excel Add-in. (The plug-in is only available for Windows; Mac users can use a PivotTable feature to replicate this.) Tableau also allows you to join multiple tables together to merge and blend data.