I adapted this example from the one included in the sf package helpfiles, which I agree is rather cluttered.
#something to start with
(sfc = st_sfc( st_point(c(7,52)),
st_point(c(-30,20)),
crs = 2264)) #some random crs other than WGS84
#transform to WGS84
st_transform(sfc, "+proj=longlat +datum=WGS84")