Last night while I was in the shower my penis erected and then my lower parts felt like they were being tickled a lot and my penis felt like it was being "pumped" or pushed more then usually (if you know what I mean), then white stuff shot out. What was that feeling? Is it normal? And was that white stuff semen?
What you just experienced is called an ejaculation. The white stuff was semen. What you felt were the muscles contracting internally to shoot the semen out. The brief, intense feeling of pleasure when the semen shot out is called "orgasm." And, yes, all of it is perfectly normal.
What it all means is that you are now physically old enough to father children, though you are probably a long ways from being ready for the responsibility of marrying and having kids. With the ability now comes responsibility. Your body doesn't know when is the right time for desiring sex and you have to train it. That will take several years.