after putting the rdata file in your working directory, do something like
load("C:/Users/1_adm.RData", ex <- new.env())
ls.str(ex)
The rdata loads variable into your workspace so that command will show you what the variable names are, so you can then use them.
I don't have the file you're talking about so I can't tell you how to access the specific fields you need.
edit
Based on your comment: Ok so the object you load is an object of type SpatialPolygonsDataFrame, and that has a Slot/property called Polygons, with objects of type Polygon. Those polygons I assume are the lat lng coordinates around the country. Accessing the coordinates should look something like
ps <- gadm@polygons[1]
then something like
ps@coords