You need a dataset file with a geographic column – coordinates and polygons – load it into CartoDB account and play with the visualisation interface to generate a map. A series of wizards can be used to create simple or category maps (displaying markers or regions coloured on the basis of explicit categories), bubble maps (markers aggregated in clusters), choropleth maps (regions coloured with a colour-scale based on a numeric variable) andtorque maps (maps that show events over time). Locations such as cities can be geolocated inside CartoDB by running a geolocation process on the geographic column, but keep in mind that only a limited number of geolocalizations are free of charge.