AND

We use "and" to connect two similar ideas.

• The girl is tall and thin.

• Sit down and tell me all about it.

• I love crème brulée and cheesecake as a dessert.

SO

We use "so" to add an idea that's the result of the first idea.

• He is deaf, so he can't hear you.

• Machu Picchu is big, so you can get lost.

• I've got an exam tomorrow, so I'm studying hard.

BUT

We use "but" to join two contrasting ideas.

• Singing rock is great, but you need a good technique.

• Penguins swim well, but they can't fly.

• I’d like to go but I’m too busy.