Working with Shapefiles
You can use shapefiles directly in R including points, polylines, and polygons. The main problem is that there are two different libraries that folks are using, "sp" and "sf". sp is older and may go away in the future. sf uses standard data vector formats and is seen as easier. Bottom line is that some packages require that you use sp while others require sf.
Other Resources
Spatial Data Tutorial - great information on sp and sf.