and: links two ideas that are related, "I like tea and coffee"
but: links a positive and a negative idea, "I like swimming, but I don't like
so: gives a result, "I was very tired so I went to sleep
because: gives a reason, "I went to the party because I wanted to see Peter"
cvičení 1 - zde, cvičení 2 - zde, cvičení 3 - zde