Wikipedia search engine string

In choosing a search engine, I found out from the directions on Firefox focus how to add them. But when they gave the string for Wikipedia, it did not work. I was wondering if any knew the accurate one and also is there a webpage that gives search strings for many apps or web pages? When I did a search under “Wikipedia Search Engine String”, I didn’t see a web page that offered it and I couldn’t find it on the Wikipedia site. If someone doesn’t mind, can you give me the directions on how to find them? I would be very grateful.