Praat is a scientific software program for the analysis of speech in phonetics. Praat analyzes mono signals. But within certain limits, stereo signals can be recorded and saved, opened, and played back in stereo. The modest support for stereo signals that Praat does provide is there for the convenience of colleagues who have their speech material in stereo form.
In fact, outside the lab, it is almost impossible nowadays to produce mono tape recordings with standard equipment and standard connecting cables. Most portable recorders record in stereo nowadays.
Do I need the 32-bit edition or the 64-bit edition?
The newer your computer, the more likely it is that it has a 64-bit operating system. If so, you can profit from Praat's 64-bit edition, which can work with larger sound files and have more than 2 GB in its memory. If you have an older computer, or chose a 32-bit operating system, the 64-bit edition will not work on it, so you have to install the 32-bit edition instead. If you are in doubt, install the 32-bit edition, because it can run on both 32-bit and 64-bit computers.