It feels different to every girl but most of the time you can't feel the blood coming out. You can only feel it when it comes out in clots otherwise you will find that most of the time you won't even notice.
You often dont feel it. Now, when the uterus lining is being shed (the reason we have a period) THAT you can feel and it hurts - worse for some than for others. If you wear a pad then youll feel the wetness eventually.