How do biologists save lives with animals

All medical research is carefully planned, and this includes medical research with animals. Experts who review a scientist’s proposed experiment involving animals weigh several considerations before approving each study. The most important thing is that the research must be relevant to human or animal health. Studies need to protect the animals’ welfare. That means that only the fewest number of the most appropriate species may be used. Under federal law, all animals must be treated humanely and undergo the least distress possible

I'm guessing you mean it in this regard:
They use animal testing with things like vaccines and cures. Say they give a rat the ebola virus - they test on them to see which cures or vaccines work, or which could possibly cause death just so they can save us humans.