Because = the reason why you do something
Why did you watch this video? I watched this video because my teacher recommended it.
Why do you watch youtube videos? I watch youtube videos because they are very interesting/funny/entertaining.
So = the result of something
My husband’s company asked him to work in Singapore, so we moved here.
I want to learn English, so I signed up for classes at ULC.
I felt sick, so I went to see a doctor.
But / Although = show contrast
I liked Mark’s video, but it was too long.
I like learning English, but I don’t understand my teacher sometimes.
Although I study English every day, I sometimes don’t understand my friends when they speak.
I went for a walk, although the weather wasn’t good.