I am drawing a bar plot of means for a diversity index for a study i have done. I have calculated the index for each sample and added it to my table (which i orignally read in). I then calculated the index means for two different environments and plotted those means. However, i cannot work out how to add error bars.i understand ggplot2 is a useful tool for doing this, but cannot get my head around the explanation.

SO, basically trying to take the means of two values from a table, and plot a bargraph with error bars. this is my code at the moment

mean Shannon of river and lake

`mean_river <- mean(parasite_data$Shannon.index[1:24])
mean_lake <- mean(parasite_data$Shannon.index[25:43])`

matrix of means #

Shannon_mean <- matrix(c(mean_river, mean_lake), nrow = 1, ncol = 2, dimnames = list(c("mean"), c("River","Lake")))

plot graph #

`barplot(Shannon_mean, 

# name axis 
    xlab = "Environment", ylab = "Shannon Diversity Index", 

# title of graph 
    main = "Diversity of Parasites found on Fish from River 
            and Lake Environments", 

# size of title text and colour of bars #
    cex.main = 1, col = "gray80")`

like i said, i have attempted to use ggplot, but cannot read the data in correctly. any help would be appreciated.