I want to know why girls bleed after or before intercourse is over?
Girls do not always bleed during or after sex.
But when girls do bleed during or after sex and it's not because of menses, then it's due to some injury in the vagina or vulva. As well, some sexually transmitted infections -- Chlamydia is a biggie for this -- can cause bleeding with or after intercourse or other kinds of sex.
The vagina and vulva are delicate, yet resilient structure made of skin, mucous membranes, muscle and so forth. The lining of the vagina is very similar to the tissue that lines the inside of your mouth. It's soft, squooshy, and it bleeds when it's cut or roughly rubbed. During penetration, the vaginal lining can get scratched or torn, particulatly when a woman isn't very aroused and lubricated or using an extra lubricant as needed. As such, it can bleed. That's why some women bleed during sex -- not just sexual intercourse either.
Manual sex or penetration with toys can cause similar abrasion. Then there's the hymen. While most women don't have much hymen left by the time they have sex, some women do experience rupturing/tearing of the hymen membrane. This can also bleed. And in especially traumatic or rough sex, women might end up with abrasions and cuts around other parts of the genitals, like the labia, perineum and anus. Likewise, all these parts can bleed when cut, too. All these cuts and abrasions? They're simply injuries.
How do you avoid injuries during sex? Do it gently and at a comfortable pace. If anything hurts, stop and readjust till it's comfortable. Use extra water-based lubricant; lube protects the genitals, and it lessens the risk of condom rupture.
And if you or your partner continue to have bleeding despite taking precautions like only entering the vagina during high arousal and using lubricant, you or she will want to check in with a sexual healthcare provider to find out what's going on.