First off the oak chips/cubes should be soaked in some sort of alcohol like bourbon to sanitize. If you want more bourbon flavor soak them for at least a week or two, otherwise less time. If you do not want any flavor other than the oak you can boil them for 15-30 minutes to sanitize.
Once done you place them into the secondary and rack the beer onto them. IDeally you want to taste your beer at least once per week to get it where you want as sometimes if left for too long it can over power the beer.