How do I fart on command?

I know burping on command is easy to do, but how do I fart on command by sucking air in my and farting it out, I have been people on youtube doing it successfully, I have been trying to figure that out for a long time, I also have been searching the web for how to do it, but a lot of the suggestions won't work, and me and my friends wants me to fart on command.