Detailed help for any QIIME 2 command can be accessed by activating a QIIME 2 environment, and entering qiime <plugin> <action> --help.
Try activating your QIIME 2 environment and entering qiime tools import --help, and see if that answers some of your questions.
There's more information on how import works in the importing tutorial. It's focused mostly on raw data imports, because most imports are raw data. It is, however, possible to import many different types (and formats) of data into QIIME 2.
Because most people import raw data (not alpha diversity results), there is no specifically tailored example in our documentation. One way to get raw alpha diversity data would be to export that data from an available artifact which contains SampleData[AlphaDiversity], look at that data directly, and then experiment with re-importing it.
Try this:
Download an alpha diversity result from the Moving Pictures tutorial - for example, shannon-vector.qza