To find the search template URL for a given web site, just perform a dummy search on this site and have a look at your web browser's address bar. For example, in case of http://www.youtube.com/ if you search for jarreau you will get this URL for the search result page:
As you can see, it contains your search term jarreau. So you just have to replace it with an asterisk to get the corresponding search template:
Other query parameters, which are separated by an ampersand (&), are often optional and can be omitted. In the above example, the aq=f parameter at the end of the URL appears to have no impact on the search result, so you can simply remove it.
The final search template URL then looks like this: