If you are introducing two guinea pigs together for the first time then it should be done on neutral territory, rather than in the hutch that belongs to one or other of them. There will be a certain amount of chasing around and teeth chattering, and if they are boars, some throaty rumbles as well. However it is very unlikely to come to battle!
Lots of food should be provided from several food bowls, and piles of greens on the floor, and then they are likely to engage in their favourite activity of eating, and where better to get to know someone than over dinner! If lots of tubes and cardboard boxes are provided as hideaways they should soon settle down together. If they are getting on too well just check their sexes again, or ask someone experienced with guinea pigs to check for you!