R offers some good resources to help you learn about its functions. For example, if you put a question mark before a function name, on the lower right quadrant of RStudio some help will pop up.
1. Type ?sqrt in your script.
2. Then, help will pop up on the bottom right hand quadrant of RStudio.
These give documentation about how to use the function, what arguments it takes, and some example code. Example code might be a helpful page to start with.
You can also precede a function name with two question marks ?? to search all of your installed packages for it.
3. Type ??read_excel.
This is useful if you know there's some sort of R function but you don't remember what package it's in. So if you get some code with the function read-excel in it but you forgot to load the readxl package, you can search for it using this double question mark and it'll tell you which one's to load.