To get into BASIC, press Control-Reset.
A ] (bracket) pompt will appear.
You'll need to boot up with either DOS 3.3 or ProDOS. You can then use the D argument with most commands. For example, CATALOG D2 will produce a catalog of the disk in drive 2.
Check out the Apple II FAQs: http://apple2.info/wiki/index.php?title=CSA2_FAQ