Potato salad is usually eaten cold, but whether served cold or just warm, which is far preferable, it should always be dressed while still hot, so that the potatoes absorb the dressing.
Boil or steam the potatoes, but do not cook too soft, or they will break. As soon as they are done, peel them and slice thinly. Put the slices in a salad bowl and pour over them the dressing, well mixed previously. Serve when lukewarm or cold. The dressing should be completely absorbed.