Thank you for the opportunity to help you with your question!
Nicotine, tar, and carbon monoxide all have one thing in common: they decrease the efficiency of the cardiovascular/respiratory systems.
When a person smokes, the carbon monoxide can bind to hemoglobin in their blood in place of oxygen, making it difficult to breathe (and therefore sometimes even fatal).
Tar is the build up on the lungs from the smoke which decreases the surface area on the lungs available for diffusion of oxygen and CO2-- also making it more difficult to breathe.
and lastly, nicotine has the ability to constrict the blood vessels in the body which decreases the amount of blood with oxygen able to get to the muscles.
I hope you found this helpful. Please let me know if you need any clarification, have further questions, or need something explained in further detail. I am always happy to help, so no need to hesitate to ask!