Go to File at the menu bar to save and export your projects. This is also where you can go to open your previous projects. When saving a project, it will only save as an Audacity project. So when you click on the file you saved, it will reopen your project in Audacity just how you last saved it.
When exporting your project to a sound file you have multiple options. MP3 is more compressed and therefore is a smaller file size.This is because it has less of the sound information on it, but it is standard enough so that it sounds close enough to the uncompressed file. WAV is less compressed and has more of the sound information on it and therefore is a bigger file size.
You also have the option to export just a selected region of your audio file with "Export Selected Audio".
You have even more options at the export menu that pops up after choosing. This also allows you to save it to a location of your choosing.
There are many different file types to choose from. This is helpful because you may want to convert your audio to a different file type for certain software, media players, or devices. Sometimes this involves a little research on what file types are supported by the software or device you would like to use.
When choosing MP3 there are a couple other options as well including exporting the whole file as a mono file.
