Thank you very much, very kind! My data was in excel format, so I imported it in R in csv format. The name I gave to the dataframe is "d". I used this commands:
setwd ('andress of my dataset')
d <- read.csv('namefile.csv', header = T, sep = ';')
d <- d[,1:21]
Then I ran some tests, and I did some boxplots (not using ggplot), but now, having to compare data on different rows, I got stuck.
I installed ggplot2, using these commands:
install.packages("ggplot2")
library("ggplot2")
Specifically of my dataset, now I should make a boxplot with rows 1 to 26 of column 20 ("experiment 1"), with a second boxplot with the rows 27 to 54 ("experiment 2"), always of column 20, to compare the two treatments.