Condoms catch the sperm and other fluids that are released during sex.
Condoms actually play two roles during sex.
First, they prevent pregnancy by not allowing sperm to be released into the woman's body. Second, they help prevent the catching and spreading of disease for both partners. Even though this is possible, condoms provide A LOT of protection . The key thing is that condoms do not allow the mixing of the fluids. This is what helps prevent pregnancy and the spread of disease.