Package development with R is a very complex topic, although it got much easier with the help of RStudio and packages such as devtools. If we want to go deeper in the package development, we can take a look at the following links:
Devtools Google Group: https://groups.google.com/forum/#!forum/rdevtools
GitHub repository of devtools: https://github.com/hadley/devtools
One of the most essential guides to package development is surely the manual on the r-project page: http://cran.r-project.org/doc/manuals/r-release/R-exts.html.
It explains nearly every aspect of the package development process in great detail.
If you made yourself familiar with package development in R and created a great package, you should think about sharing it with the whole R community by submitting it to CRAN. You can do it via an online form at https://cran.r-project.org/submit.html.
But before you upload your package, you should read the CRAN repository policy carefully and check that...