Once you reach Bhuntar the next morning, board the bus till Barsheini. Its a two and a half hours journey. The whole journey will be along the Parvati river. If you don't get a direct bus till barsheini, deboard at Manikaran and wait there for the next bus. At Manikaran, the Gurudwara offers free meal and decent accommodation for the night which is also free. Its better to have your brunch here. The food is basic but nutritious. There is a bus that goes from Manikaran to Barsheini around 12:00 pm. Through local buses, you wouldn't be spending more than 100 rupees to reach Barsheini from Bhuntar. The cheapest way is obviously Hitch-Hiking!
You'll reach Barsheini bus-stop at noon. There are options to drop some of your luggage here for a couple days for Rs 80 or less. There are restraunts here and toilets if you need to freshen up a bit. From the bus-stop, you have to walk for 700ms till the big hydro-power project. The dam is exactly the point from where the Trek starts.
The Trek till Kheerganga is 10-12kms in length. There are two routes to do it. I will explain the difference in a while. But first you need to make a choice. Do you want to start the trek on the same day itself or go to a nearby village, spend the night, relax, and start the trek on the next day. I would suggest you the latter.
The trek is not easy by either of the routes. It can be classified somewhere between easy and moderate. It takes 5-6 hours to reach there. If you are used to any of outdoor sport or walk or hike often, then it will be easier and wouldn't problem you much. But if you are not into physical activties much and this is your first trek, then I would suggest you to trek the next day.
The trek from either routes has a marked trail and doesn't need any porter or guide.
There are two routes to reach Kheerganga from the dam at Barsheini. But there is a third road that goes upwards from the dam towards Tosh. This route doesn't take you to Kheerganga. This is for the ones who want to go to Tosh.
Tosh is a village with a lot of cafes and guest houses for food and staying options. It is 4kms from the dam at Barsheini. There is another 'local route' from the Barsheini bus-stand which is shorter, steeper and not marked properly. If you are with a local, then only take this route.
The main road to Tosh from the dam is motorable. You will get shared cabs from Barsheini charging around Rs150 per person. You can either go by the shared cab or take the 4km hike for an hour. The hike is along the road and not very difficult. If you are not very tired and want to save money you can take the walking route. Just ask yourself that if you want to walk on a plain concrete but uphill road for an hour.