Brilliant, you can now record!
I've also got a good guess about why it works now and why it did not before.
Am I correct in thinking that the microphone that did not work plugged into a USB socket (flat rectangular plug/socket) and the new microphone that does work has a small round plug that goes into a small round hole on the sound card?
When you select "Save", Audacity saves the "Audacity Project". This is NOT an audio file and will not play in any software other than Audacity.
Audacity projects hold much more information than a normal audio file. For example, if you have a project with multiple tracks, then each track is saved independently.
To get a normal "audio file", you need to click on "File > Export".
In Audacity 1.2.x there are 2 relevant options:
"File > Export As WAV"
"File > Export As MP3"
For licensing reasons, Audacity is not allowed to ship with MP3 encoding built in. MP3 encoding is provided by adding the "Lame Encoder".
How to install "Lame" is covered in the "Frequently Asked Questions" (FAQ) section of the main Audacity site.
http://audacityteam.org/help/faq
The FAQ section is well worth a read as it will cover many of the questions that you are likely to have.
There are also some good "Tips" and "Tutorials" (see links at top of this page) that will help you to become an Audacity expert.
Aixa wrote:2- Why is it 7.93-7.96 MB i
Uncompressed audio makes BIG files - that's why MP3 and other types of compression are used for sending audio by e-mail or over the internet.
Uncompressed audio is better quality than MP3, but CD standard audio uses about 10MB per minute of recording time (about 8 times more than an MP3)
Aixa wrote:3- If I read it correctly, it recorded it in Stereo, 44100 Hz, 32 bit float, which must be the default settings, as I made no changes. What are the appropriate settings for an MP3 voice recording where sound quality is not important as long as it is intelligible?
Yes that's the default. This allows you to work in high quality and only suffer the audio damage at the Export stage, rather than compounding the loss in quality with everything you do in Audacity. Lame should automatically adjust the settings when you export as MP3.
The best settings for what you are doing are "mono 44100Hz 16 bit".
Also, for small MP3 files of your voice recordings, go to the "File Formats" page and set the MP3 bit rate to 64 (I'm assuming that you are using Audacity 1.2.6). This setting is only available after Lame has been installed.