A few paths for you to explore:
No package needed
d <- data.frame(Address = c("1'00-SV", "2'00-SV", "3'00-SV", "21'00-SV"),
MonthAvg = c(6.1, 5.6, 21, 13))
barplot(MonthAvg ~ Address, data = d)

plot(MonthAvg ~ as.factor(Address), data = d)

plot(MonthAvg ~ I(1:nrow(d)), data = d, axes = FALSE, xlab = "Address", type = "b")
axis(side = 2)
axis(side = 1, at = 1:nrow(d), labels = d$Address)

Using package {ggplot2} from tidyverse
library(tidyverse)
d %>%
ggplot() +
aes(y = MonthAvg, x = Address, group = "") +
geom_point() +
geom_line()

Created on 2019-10-23 by the reprex package (v0.3.0)