How can a boy lose the virginity?

Simply, having a sex. I know that there are so many questions such are "how does a guy lose virginity" or how to lose virginity for men but generally, there is no a proper answer. I once was reading about this and I can tell you that virginity is actually an arbitrary construct, but the best definition is that a guy would lose his virginity after putting his penis into the vagina of a woman - that is the best, shortest and the most informative explanation. For example, I have never noticed when my bf lost his virginity, he told me later that I was the first to him. 

Thank You, Sir.

I lost my virginity at age 14, to a girl who was only 15 and a half. Both of us were virgins and we both had a nice time together. It was a tight fit, but we loved it.

Unlike breaking of the hymen, ejaculation can happen through sex or masturbation.

There isn't any physical way to know if a boy is a virgin.