Hi Lucy, welcome!
The code you have shared is not reproducible, and you didn't wait for the image to finish uploading so we can't see it either, so I'm guessing here, but I think this what you are trying to do.
library(ggplot2)
counts <- data.frame(type = c('C','M','N'),
respiratory_rate_mean = c(18.667,19.167,19))
ggplot(counts, aes(x = type, y = respiratory_rate_mean)) +
geom_col() +
labs(title = 'Respiratory Rate Mean vs Nicotine Type',
x = 'Nicotine Type',
y = 'Average Respiratory Rate')
Created on 2019-01-24 by the reprex package (v0.2.1)
For future posts please read this FAQ about making a reproducible example (like the one I did above)