functions st_transform and st_point

Hello   I'm trying to work out ways of manipulating maps in R and have
found various potentially useful starter sites, eg

https://r-spatial.github.io/sf/reference/st_transform.html
p1 = st_point(c(7,52))
p2 = st_point(c(-30,20))
sfc = st_sfc(p1, p2, crs = 4326)
sfc
st_transform(sfc, 3857)

and
https://rforjournalists.com/2021/04/10/how-to-plot-a-large-rural-area-using-ordnance-survey-data-in-r/
But when I try to run the example code R tells me that it cannot find
function "st_point" (or in  the other instance "st_transform")   I assumed
that these functions were in some package, and searching I found "sf" and
"lwgeom" suggested, but installing and loading these does not help.  Does
anyone know where I can find the wherewithal to make these st_ functions
work?

Thanks Nick Wray