There is a confusing word – A in the Russian language. It can mean as “and” so “but” in different context. Let’s consider when we have to use А. The difference is here: И is used in enumeration and imperative mood, А is used in other cases.
Сходи в магазин и купи арбуз. – Go to shop and buy a watermelon. This is an example of imperative mood.
Купи арбуз и картошку и масло. – Buy a watermelon and potato and a butter. This is an example of enumeration.
Я и ты. I and you.
Now let’s see some examples of А:
-Привет, как поживаешь? – Hello, how are you?
– Хорошо, а ты? – Fine, and you?
As you can see, this is neither enumeration nor imperative mood in this example. As you could see in the beginning of this article – A can also mean “but”. Here are two examples:
Она просила его подождать, а он уехал. – She asked him to wait but he has gone out.
Ему предложили поехать на дачу, а он не хотел. – He was asked to go to the country house but he didn’t want.
In these cases А is equal to НО that means “but”.