If you are loading PIL.Images, torchvision.transforms.ToTensor() will create a normalized tensor with values in the range [0, 1].
torchvision.transforms.Normalize() will create standardized tensors with zero mean and a unit variance.
Usually you would use the mean and standard deviation from the training set.
However, often the ImageNet statistics are used for RGB images, especially if you are using a pretrained model (same input statistics) and if your dataset is similar to ImageNet.