Entering Commands in RStudio –
When you start RStudio the main window on the left is a R Session. From there you can enter commands interactively directly to R.
R prompts you with > (greater than sign). You can type any expression here and R will evaluate for you.
Let’s say you want to add two number 5 and 6 together.
We can see the result is 11. And if you look carefully you can see  before it. To R the result is a vector which have only one element int it. R labels the value with  to signify that this is the first element of the vector.
R will prompt you for input until you type a complete expression. The expression max(5, 10, 20) is a complete expression so R stops reading input and evaluates what it’s.
> max(5, 10, 20)  20
In contrast, max(5, 10 is an incomplete expression, so R prompts you for more input. The prompt changes from greater than ( > ) to plus ( + ), letting you know that R expects more.
> max(5, 10, + 20)  20