i have used foobar2000 for a long time, but i really don't know.
can i do this from "file" menu?

You can use drag&drop from Explorer to add them to the playlist.

Thanks foosion. It wroks. Is an easier way? I mean can this be done in foobar without explorer or something like that.

You can add an entire folder structure, including all sub-folders using Add Folder....



If you only want to add certain sub-folders, then you must do as foosion has said.

You can add multiple folders at the same time from command-line, though.
If you have some common task you want to accomplish, an extra shortcut with target like this might work for you:

Using explorer is 100% exactly as easy as using an "Add Multiple Folders" dialog. In both cases you launch an explorer window, look for your folders, select them and then add them. There is no speed benefit. In fact, there's a speed loss, as the standard explorer file dialogs have such limited browsing functionality compare to the main program with its folder tree.

Use album list as a panel. set its view to: by folder structure. Here you can select multiple folders at once by shift or ctrl-clicking.

You need the latest foobar for that and all musicfiles need to be scanned to your library.

Also:
You can use facets the same way. Set first facet as Folder and ctrl / shift click will work there too.