You can reach Kasol either from Delhi or Chandigarh whichever is suitable to you. We were coming from Mumbai so opted for Delhi route. For Kasol, you need to book tickets in advance from Delhi to Bhuntar which can be easily done through Himachal Tourism site http://www.hrtchp.com/hrtctickets/. Every Manali /Kulu buses goes via Bhuntar. HRTC buses very comfy and good for a the night journey. You have to take buses from Delhi Kashmere Gate. The place is very crowded and messy so reach at-least 30 minutes before , they are very punctual and will not wait for anyone.