Hey!
You kinda got it right in the last line in the console in your snapshot.
So, you should do sth like this
VOM_plot<-ggplot(data = dat, aes(Month, VOM))
VOM_plot
However, this won't show anything, since you are not specifying any geom. For instance, you could have a simple scatter plot like this:
VOM_plot <- ggplot(data = dat, aes(Month, VOM)) +
geom_point()
VOM_plot
HTH