Here is the answer to one of the most frequently asked questions - What's the difference between И, А, НО in Russian and how to use them?

The most mistakes come up in usage of И and А, because they both are usually translates as "and" in English. The main idea that you need to understand is that И is like a +, it's used to sum up things, to put them together, to the same position.
А is used to show the difference and contrast between people or things.
НО is usually a contradiction, which is pretty similar to English "but".

Some examples

Маша и Саша любят яблоки. - Masha and Sasha like apples (they both have the same feeling towards apples, the sentence shows that two people are similar)
Маша любит яблоки, а Саша нет. - Masha likes apples, and Sasha doesn't. (Two people have different feelings, they are not similar, but different)
Маша и Саша любят яблоки, но не любят бананы. - Masha and Sasha like apples, but don't like bananas.

And finally the most frequent error the foreign students have when they learn Russian

If you want to ask "And you?" as a return question - use A, not И!!!!

• Как дела?
• Хорошо. А у тебя?
• Тоже хорошо. Как тебя зовут?
• Лена. А тебя?
• Костя.
• Ты из Москвы?
• Да. А ты?
• Я тоже