Pour a generous shot of Brandy over some ice in a rocks glass and fill with sweet & sour. Traditional garnish for a drink using sweet and sour is a maraschino cherry.
You can purchase sweet and sour mix at grocery stores, it's usually near the sodas with other mixed-drink goodies like Grenadine, Roses' Lime, Bloody Mary mix, etc.
You can also make sweet and sour mix yourself. It's basically one part simple syrup to one part lemon and/or lime juice. (Simple syrup is just a one to one ratio of sugar to water, which you bring to a boil to dissolve the sugar.) You may have to play with the ratio of lime/lemon juice and simple syrup to get the right mix of sweet to sour depending on the fruit you use.