If you type in the search words "hymen gallery" you can find diagrams of hymens.
The best way I can describe it is to imagine that there is a mini donut at the entrance to the vagina. There is a hole and the 'donut' is a thin piece of tissue. When there is no sign of the donut, or very little of the donut left, the hymen is gone.
And the hymen is not an all or none thing. There can be some of it remaining, meaning there is a larg hole/ opening or very little of it remaining, like a very thin donut.