Music streaming is only available if you buy the streaming app, which is optional.
The Ubuntu One apps create a folder on your computer or mobile device with which you can sync files. However for Windows users that’s a significant limitation in that the only files that Ubuntu One will let you sync are those that are located in your Home folder. This follows the Linux convention where users don’t normally have any accessible space anywhere outside of the Home directory. In Windows, however, the Home folder is a relatively recent development, and storage of data files elsewhere is common.