Female guinea pigs are generally easier to introduce as they are less terratorial than males - not always, but often. Here I've got some help for you:
First, bring them to neutral territory, such as a bath tub, a bed or somewhere they've both never been. Make sure you have a chicken wire wall in between them. Let them sniff each other and get to know each other. If this is going fine you can eventually remove the chicken wire. They may be raising their hackles up or teeth chattering at first, but if it doesnรขโฌโขt lead onto anything them they should be fine. If they go for each other, then take them out and bath them both (at different times) so they smell the same. Then re-try the first steps. It is a general rule that females will get on better and be less likely to fight than males. It is said that males do get on better when there is one younger and one older though รขโฌโ the dominance thing is easier for them to sort out. Remember you must clean out the cage thoroughly and remove any scents before they go back in or the older one may become territorial.
They can eventually go in the same cage and become buddies for life! Good luck!