There's more

Installation is also possible via RStudio features, which may seen more user friendly for newcomers. Open your RStudio, go to Tools > Install Packages..., type the packages' names (separate them with space or comma), and hit install. It fills the install.package() function and shows it in your console.

This is most indicated when you are not absolutely sure about the package name, but have a good clue. There is automatic suggestion thing that shall help you out to figure exactly what the package name is. You can also install packages from local files by using this feature. Look for an option called Install from and switch it to Package Archive File instead of Repository.

RStudios also gives you a Check For Packages Updates... option right below Install Packages... Hit it once in a while to make sure your packages are properly updated. Along with the packages to be updated it also shows what is new about them.