Conjunction А [A]
This conjunction is used in opposition of different subjects, objects or persons. This is a milder form of opposition. In addition, it can have connective meaning:
Это дом, а это сад. [Éta dom, a éta sad.] – This is a house and this a garden.
! In this case, the question is about different objects located in the same area.
Я смотрю телевизор, а жена читает книгу в соседней комнате. [Ya smatryú tilivízar, a zhiná chitáit v sasédnij kómnati.] – I’m watching TV, but my wife is reading a book in the next room.
Conjunction НО [NО]
This conjunction is used in opposition of different features of the same object, subject or person. This is a morepowerful form of opposition. It has no connective meaning; rather the maximum distances the same object, subject or person:
Моя машина исправная, но уже очень подержанная. [Mayá mashýna isprávnaya, no uzhé óchin′ padérzhanaya.] – My car is working, but very used.
Моя тётя любит свою работу, но у неё маленькая зарплата. [Mayá tyótya lyúbit svayú rabótu, no u niyó málin′kaya zarplata.] – My aunt likes her work very much, but her salary is small.