Most condom failures are the result of improper usage.
The package should be opened on the edge, not down the middle, to avoid tearing. If there is a receptacle end on the tip, it should be squeezed lightly while rolling the condom on, so there is no air trapped in the condom. That's important because trapped air will tend to make the condom bust during intercourse, like a balloon that's being squeezed. Your partner can do this, or you can. Soon after the man ejaculates or cums, he needs to reach down and hold the rim of the condom on the penis while the penis is withdrawn from the vagina, so the condom doesn't slide off and stay inside her.