Like retired1af says, it's not necessary to install from scratch. If, however you decide you want to try anyhow, the first step would be to look what's inside the file (.tar.bz2 is just a zipped archive file, if you extract it you'll get files and directories).
Some programs may be able to look directly inside the file (like Xarchiver which comes with VL7). Or, you could open a terminal/console and unpack it manually. First, change directory to the directory where you downloaded the file to (for instance /home/user/downloads) using the command 'cd'.
Next, unpack the archive as follows
tar xvf wxPython-src-126.96.36.199.tar.bz2
Usually, there's a README or INSTALL file in there that you can read. I cheated, and googled instead