Using the DATA LIBRARY tab, add the Portland building footprints to the map. Select the data set from the list, and then push Create Map. The dataset will be added to the account datasets tab, and to the map creation interface called Builder:

The dataset is added as a layer to the map. All aspects of the layer can be manipulated in the map editor, including the color of the layer, the attributes shown, the pop-up window, and more. The basemap can also be adjusted. 

Widgets, representing live data from attributes, can be added as well. I've added the US Census Tracts layer from the DATA LIBRARY to the map, and added a graphing widget that will display values from a selected attribute field. This graph is dynamic, and will adjust the values displayed based on the specific census tracts which are shown in the map window:

Check out the other tabs in Builder, including DATA, ANALYSIS, STYLE, POP-UP, and LEGEND, to further customize the map. There are a number of adjustments and widgets that will make the data interactive. The map can also be made either public or private, and can be published to the web by pushing the PUBLISH button. CARTO's editors and data ingestion interface make it really easy to create and share maps.