A conjunction is a word used to connect other words, phrases and clauses together.

'Or' is used to express choices.
Example -
1. Do you like playing football or badminton?
2. Would you like tea or juice?

'So' is used to link between cause/ reason and results
Example -
1. He’s hungry so he gets some food.
2. He lost the key so he couldn’t get into his room.

' Because' is used to give reasons.
Example -
1. She doesn’t go to school because she’s sick.
2. Because it rains, I wear a raincoat.