In R, you can use the mean() function to calculate the mean of a numerical vector, and the sd() function to calculate the standard deviation of a numerical vector. Here is an example:

# Create a numerical vector
x <- c(1, 2, 3, 4, 5)

# Calculate the mean
mean(x)

# Calculate the standard deviation
sd(x)

You can also use the summary() function to get the mean and standard deviation together with other summary statistics of a numerical vector.
There is also a package called psych which has more advanced functionality for calculating descriptive statistics, like describe() function which gives a more detailed summary of the data.

library(psych)
describe(x)

You can install the package by using install.packages("psych") and load the package by using library(psych).