I know its supposed to come naturally. But i don't understand, how do you know if its coming out without force??
btw im 15 about to be 16 in may, if that helps.
Vibrato is an effect which happens one day when you notice suddenly that it has happened. Pop singers often have the unfortunate habit of tightening everything up in their throat and forcing out an unpleasant wobble. This is NOT true vibrato.
When your voice has developed more, and after a good period of training, the vibrato is noticeable as a new resonance in your voice. The long notes develop a "ring" to them. It doesn't have time to develop on short notes. Your control and breath support is starting to work, resulting in pitching being accurate and stable. Imagine that the note you are singing is on a straight line. The "ring" is as if the note is fluctuating a tiny fraction and absolutely equally cross both sides of this line. It is quite unlike a trill where the singer is deliberately singing two notes alternately and very fast. Trills are generally expected in high voices – sopranos and counter tenors especially, and they take a lot more training to be possible.
You really will notice when you surprise yourself with the new richness and expressive depth in you voice. After this, you will never not have it. Most importantly – don't try to force it, wait patiently for it to happen and it will.
Find yourself a singing teacher if you haven't got one already. Only a good teacher can help you get the best out of your voice.
Best wishes for your singing future.