You should probably not have to do anything special other than using the normal newline character. When you retrieve it from the DB and want to display the data, then you might want to replace the newlines with HTML <br /> tags, which may be most easily done within your application code rather than the SQL. For instance, in PHP you can use the built-in nl2br() function:
echo "<p>" . nl2br($text_from_database) . "</p>\n";
You might ask, "Why not just insert the <br /> tags into the database field?" If you do that, then you have output-specific data in there that you might not want in future uses of that data, which might mess up search functions you need to run on the data, etc.