How to plot a histogram of a specific data frame column in R

Question

I am super new to coding with R, Im taking is as part of a bachelors degree program. I am super stuck on something I feel should be basic but I cannot get my code to work and I am not sure why. The prompt is:

"In this problem we will be using the mpg data set, to get access to the data set you need to load the tidyverse library. Complete the following steps:

Create a histogram for the cty column with 10 bins"

and for my code I have:

library(tidyverse)

print(mpg)

df <- mpg[ , c("city")]

histo <- ggplot(data = df, aes(x=median)) + geom_histogram(bins=10)

print(histo)

The first print was just to make sure the data loaded correctly, which it did. I am not sure about the second print function, the histo one. Ive gotten various error messages or bugs so Ive been just moving stuff around and trying different commands to get it to work. Im following the steps previously outlined in our reading, but I cannot seem to get this to work. Any help would be appreciated.

I have tried removing the print(histo) function and just leaving the ggplot, but that give me a blank white box instead of a plot, or no plot is printed.