@nobuaki-h You only need to mark the checkbox "Save metadata with file" in the Save As... dialog and all metadata under View > Metadata > Show All will be embedded into the file (if the file format supports it).

To create a selection with a specific number of samples make a right click on time text boxes in the bottom right corner of a audio file window and click on Set Selection. You can change the dialog input format to samples.

You can convert the selection to a sample loop via the View menu. A file can only have two sample loops, a sustaining loop and a release loop. You can fine tune the loop points with View > Loop Tuner.