It depends on what skin your using as to where you will find the code.
If you are using the jrElastic skin then look in the:
index.tpl file via either the template editor in the ACP or changing the .tpl file in the file system.
The code for a list looks like this:
{jrCore_list module="jrVideo" order_by="_created desc" template="index_list_videos.tpl" limit="5" require_image="video_image"}
That piece of code reads
"Get me a list of the jrVideo modules items. order them by the date they were created with the newest first. only get me 5 and make sure they each have an image. I want to customize how the output looks, so check the index_list_videos.tpl file for layout instructions."
There is more info on using the jrCore_list function here:
"{jrCore_list}"
http://www.jamroom.net/the-jamroom-network/documentation/development/89/jrcore-list
You will want to change it to something like:
{jrCore_list module="jrYouTube" order_by="_created desc" template="index_list_youtube.tpl" limit="5" require_image="video_image"}
That file index_list_youtube.tpl probably doesnt exist, so you will need to create that if you want a custom layout. If you leave it out, you get the default layout.