Does it help if you do this trick or something like jumping up and down???
Theres a lot of BS being posted on this topic. Don't take my word for it – read Richard Miller, who is the top vocal pedagogist in the world. Vibrato comes from knowing how to close the vocal cords when singing and maintaining the right amount of tension while the breath flows through. It is learned in so much as you need to learn to adduct your cords before vibrato comes naturally. Anybody can have natural vibrato, but it takes a while to learn the correct vocal posturing and balance of muscles and breath in order to do it. Conversely, a great many people do not know how to do this and artificially put in a fake vibrato which is not natural, and sounds like garbage. It also wrecks the voice over time.
The best way I can liken vibrato to something you can do outside of the vocal cords is to push your hands together and push equally on both hands so that they meet in the middle and then push harder but do not let one side or the other push harder. Hold them like that for a few minutes and the muscles in your hands begin to shake. This is what your cords do when singing with vibrato. You must have enough tension without overdoing it, and the muscles naturally wobble to produce the vibrato as you let the breath flow through. Without bringing the cordss together while singing, you can now see why vibrato would be impossible.