If you're familiar with Object Oriented Programming (OOP) languages, then there are chances that you at least know the words "packages" and "classes"; if that's not the case, don't panic, you are going to learn all of it here.
Packages are a convenient way of splitting code into groups. Doing so, allows one to have several classes with the same name in different packages. This can be really useful, as you may, for example support two scripting languages in an application and need to write an interpreter class for each one.
Packages are represented by folders under your source directory on your filesystem. Each package has a path, which is a string obtained by joining the folders' name with dots. So, for example, if your source folder is /dev/myProject/src and you have a folder /dev/myProject/src/proj/dao, you have a package whose path is proj.da (you also have a package "proj"). There's a special package that has an empty path; it is named the top-level...