Hi @tung134679!
Welcome to the RStudio Community!
Here is an example using ggplot and geom_sf,
with the rnaturalearth package and rnaturalearthdata,
to help you get started.
library(tidyverse)
library(sf)
#> Linking to GEOS 3.7.2, GDAL 2.4.2, PROJ 5.2.0
library(rnaturalearth)
library(rnaturalearthdata)
library(rgeos)
#> Loading required package: sp
#> rgeos version: 0.5-2, (SVN revision 621)
#> GEOS runtime version: 3.7.2-CAPI-1.11.2
#> Linking to sp version: 1.3-1
#> Polygon checking: TRUE
viet <- ne_countries(country = 'vietnam', type = 'countries', returnclass = 'sf', scale = 'medium')
ggplot(data = viet) +
geom_sf() +
geom_point(aes(x=105, y =22), size =2, shape =23,
fill = "blue") +
labs(x = "Longitude East", y = "Latitude North",
title = "Map of Vietnam", subtitle = "with arbitrary point",
caption = "data from rnaturalearth mapped with ggplot2 and sf")

Created on 2019-10-18 by the reprex package (v0.3.0)
I found this web post helpful in making maps with sf.
https://www.r-spatial.org/r/2018/10/25/ggplot2-sf-2.html
It will help you to get answers to your R questions if you can learn to make a reprex.
A reprex is a reproducible example. This is a nice guide to making your own reprex. This will help you for future questions.
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