If you are a complete beginner, then start learning the basic concepts of the R language, such as data types, functions, data structures, variables, and operators. Also, you must learn how to build graphs and plots for data visualization as it is the most important area where businesses rely on. You have to implement the codes of R using RStudio, which you can download from rstudio.com. You should also focus more on implementing data manipulation, exploration, and visualization techniques. This will help you get a good start and a hands-on experience in R programming.
If you are looking for an online course to learn R programming, check out this R Programming Online Course by Intellipaat.