I adapted this blog post from a chapter in my upcoming book, R Programming in Plain English. You may download a PDF of all completed material for this book here.
Packages are one of the most important concepts in R programming. It's almost hard to conceive R programming without them.
An R package stores various functions and data sets for other users to access. It allows R to move beyond its roots in statistical programming and achieve more complex goals.
For example, you might be writing a research paper. You want to clearly show the results of your regression analysis in this report, along with various tables and charts to illustrate key points. You can use a combination of Rmarkdown, ggplot2, xtable, and various other packages to accomplish this goal.
That way you don't have to copy and paste your work to a word document as you analyze the results. You merely write it and program it in R and then export it to Microsoft Word when you're done. This saves you a lot of time in the long run and makes your code far more re-producible.