Here are a few tips that it would be best to read before bringing your new pet home.
A male guinea pig and a male guinea pig CAN be housed together only if introduced at a young age. If you introduce two older males to one another they will fight causing terrible injuries to each other and you if you try to break up the fight.
Females can be introduced young, to a younger guinea pig or old if they are sisters. Introducing two completly different adult female guinea pigs can cause fights as terrible as the males.
Do not breed a male pig then introduce him back to his male friend, they will not remember each other and will fight.
Sexing a guinea pig is quite simple, females have flatter "Y" shapes while males have bumpier "i" shapes. If you are still unsure of the sex or your pig be sure to sex it properly before purchasing another pig. This website will help you sex your piggy friend too!