I dont know that why do valentines day is celebrated ?

There is so much talk about Valentines day everywhere, news channels, news paper, online websites, magazines.. every one is talking so much about it... but I don't understand what is the need to celebrate it? Is it a festival or a n obligation?

or people need a way so that they can express their love ? But love is there when you fall , love don't need any medium, one can fall in love anytime and one can love anytime. Why need of a day. kiss day, hug day, ye day, wo day..But why need ?

You have already answered this in your question, Valentines day is just another day but it is supposed to be a day where people express their feelings to other, so it can be motivation to those who are unable to do so, encouragement to mend broken relationship and more.

And because, somewhere everywhere is in love with someone or was in love so it makes sense for everybody and its the reason its so widely acclaimed and celebrated.