The `mutate()` function is a part of the dplyr package in R, designed to create new variables or modify existing ones within a data frame. It allows users to perform calculations and transformations on columns, making data manipulation straightforward and efficient. When using `mutate()`, you can specify the new variable name and the operation to be performed. For example, you can add a new column that is the result of a mathematical operation on existing columns. This function is particularly useful for data analysis and preparation tasks in the R programming environment.