You need to transform your data into a longer format if you have the values you want plotted in different columns. ggplot2 likes working with long formatted data, so learning data transformations is key to ggplot success.
library(tidyverse)
# Create the data
data <- tibble(
a = 8,
b = 10,
c = 13
)
data
#> # A tibble: 1 x 3
#> a b c
#> <dbl> <dbl> <dbl>
#> 1 8 10 13
# Make the data long,
# Transforms the data to something ggplot likes
data_long <- data %>%
pivot_longer(everything())
data_long
#> # A tibble: 3 x 2
#> name value
#> <chr> <dbl>
#> 1 a 8
#> 2 b 10
#> 3 c 13
ggplot(data_long) +
geom_bar(aes(x = name,
y = value),
stat = "identity") # use value from the data

Created on 2021-08-19 by the reprex package (v2.0.0)