shrink transaction log in sql server

DBCC SHRINKDATABASE (db_name, size)
1    Is this mean i am shrinking whole database or only transaction log file ??
2    If i am shrinking whole db then is it good to shrink only log file ?? By using ssms 
     (right click db -> tasks -> shrink -> files -> log) and not by this command.
3   If i want to use above command how to determine the size to specify ?
4   Is there any other way to reduce log file size other than shrink ? i took backup of 
    log file but it never reduced the size.

h2007