This page explains how to display a background map with the leaflet R library? First initiate the map with the leaflet() function. Then add tiles with addTiles(). With leaflet, we can use the %>% operator to pipe functions. Here you can see how to get the same result using or not this operator. By default, you get the above map. See graph #179.2 to see how to zoom on a zone, and graph #180 to learn how to change background.
# We always initiate a leaflet map with the leaflet() function
# Then we Add default OpenStreetMap map tiles
# Same stuff but using the %>% operator
m=leaflet() %>% addTiles()