[dba-SQLServer] Question about Error Logs

I don't understand how the SQL error logs work. The last error log I have is
dated 8/21/2008. Does the database engine create an error log only when
there is an error or a warning? I had assumed that it would create one every
day, even if only to post a message that there were no errors, but maybe
that assumption is self-contradictory.

Arthur