I will try to answer. So, physically, there are two main reactions to smoking, depending on how long it is since you last smoked.
If it's over a long period there is a 'head rush' - a pleasurable feeling of giddiness and 'floating away' - I haven't tried other drugs, but I imagine along the lines of, although possibly not as intense, as popular street drugs. The smoke wisps and curls creamily around you and you sink into a lovely haze for a while.
If it's not over a long period, what happens is you develop a craving - a sort of 'hunger' for the cigarette/tobacco, and so when you smoke, you get the relief of satisfying the craving, a physical and mental sense of satisfaction and relief - an 'aaah' moment. Like a cold drink on a hot day.
But it's not just a physical pleasure. Smoking can give you a moment to yourself in a crowded day, or it can be a social thing - smokers chatting outside the pub. Since it has become so frowned upon, there is a lot of cameraderie amongst smokers.
It can be a useful stress reaction - along the lines of a 'nice cup of tea' or, for some, pouring an alcoholic drink. 'This terrible thing has happened, I'm all over the place - I will have a cigarette'.
I'm not trying to 'sell' smoking - it's terribly expensive, it's bad for your health, in many ways it's inconvenient - always needing to make sure you have enough tobacco, worrying you'll run out at a bad time (I have 'emergency' tobacco at home strictly to be used in life or death situations, the last time I used it was when my dog suddenly died a few years ago). People hate you for it. People tar you with a brush - assuming you'll smoke all over their newborn babies (I don't) drop your cigarette ends everywhere (I don't) and generally be inconsiderate (I try not to be).
But there you are - you asked, I hope that's enlightening.