[OJS 3.1.2.4] Welcome note on journal homepage

Hi @kkaegeumna
That site seems to be a Wordpress CMS. I am sure there are many plugins that will do that job. If you specifically ask for a homepage slider for OJS 3, there is one. I use a commercial OJS theme developed by Openjournaltheme (@navotera) on my journal.
Regards,
wp