There is no Train track to Kullu Manali. You cannot go directly from Delhi to Manali on Train.

If you are planning to travel by train from Delhi or any other city. You have to go get down at Chandigarh. From there you can catch Volvo bus to Manali or hire a car for complete trip.

You can also get down at Joginder Nagar and from there you can hire a car as well.

Reaching Kalka is a bit off the way. If you are planning for Shimla and Manali tour then reaching Kalka is a very good option. You can go Shimla by Toy train and then after staying at Shimla you can proceed to Manali. In return, you can get down at Chandigarh or Delhi.