So, what's the real story on Python 2 vs Python 3?

[Travis McGee]

The Python.org site says that the future is Python 3, yet whenever I try 
something new in Python, such as Tkinter which I am learning now, 
everything seems to default to Python 2. By this I mean that, whenever I 
find that I need to install another package, it shows up as Python 2 
unless I explicitly specify Python 3.

What's the deal? If I want to make a distributable software package, 
should it be 2 or 3? Enquiring minds want to know.