For finer control over audio I/O, open your system's Sound control panel or the control panel that came with your sound card.
Mono recording is not the same on all computers or sound cards. Sometimes recording mono only records the left channel, and sometimes it mixes the left and right channels.
You may notice that when you play the two tracks you recorded together, they aren't synchronized. This is unavoidable to a certain extent, though future versions of Audacity may try to minimize it even more. To fix it, you will need to grab the Time Shift tool and slide one of the tracks around until it sounds right.
Note that this is not the same as playthrough, which means having the computer play the track that you are currently recording, as you are recording it. You may be able to enable this using your operating system's Mixer or Sound control panel, but Audacity does not have an option to turn on Playthrough directly.
If you have a fast computer and enough disk space, you should always use 32-bit float samples while editing, and then export your final mix as a 16-bit WAV file (the default).
To reset to Audacity's defaults, press the Defaults button. This will get rid of any changes you have made.
If you have customized your keyboard layout and want to share it with someone else, you can press Save... and save your complete keyboard layout as an XML file that you can share. To load an existing layout, press the Load... button and locate the XML file.