You don't say how much KBr you purchased. To make a 10% w/v (weight/volume) solution you would dissolve X grams of solid in enough water to make 10X milliliters. So if you purchased 100 grams of KBr you would dissolve this in enough water to make 1000 milliliters. If you purchased 50 grams then you would use enough to make 500 milliliters. For a 10% solution every milliliter will contain 0.1 gram of solid.