Read the box. The package should say if the condom prevents sexually transmitted diseases. Currently the U.S. Food and Drug Administration recommends latex condoms for this purpose. The FDA also has approved several polyurethane condoms for people who are allergic to latex. Condoms that do not cover the entire penis should not be used to prevent disease or pregnancy.
Some packages also show when the condom was manufactured.
Date of manufacture is not an expiration date. Store condoms in a cool, dry place out of direct sunlight. Your pocket is not a good place to carry a condom. Neither is your glove compartment. Extreme heat and cold can make latex brittle and gummy.