There are two types of spatial columns that we'll discuss in this course: geometry and geography. We'll explain the difference between these two types later. For now, keep in mind that both of these types can be used to do similar things, but
geometry is quicker, and
geography is more accurate. For the vast majority of this course, we'll focus on geometry. In PostgreSQL/PostGIS, there are no specific column types for points, lines or polygons. Instead, they're all stored in a single column type called geometry. Inside PostgreSQL, in turn, these geometry columns are stored in an internal format which is only understood by PostGIS and looks like: 3F545952C0CBDE2613B7C84...
Fortunately, PostGIS makes it possible to convert its own internal format to something we can actually make use of. There are quite a few text output formats, such as Well-Known Text (WKT), Well-Known Binary (WKB), Geographic Mark-up Language (GML), GeoJSON and others.