. They decided to go on an excursion. They want to get away from work stress

=>They decided to go on excursion because they want to get away from work stress.

. My father taught me how to use the computer. Before that, i didn't know how to use it

=>My father taught me how to use the computer because before that,I didn't know how to use it.

. I arrive at the station. I will call ou right after that

=>I arrive at the station,so I will callyou right after that.

. My brother is very out-going. I am quiet reserved

=>My brother is very out-going,so I am quiet reserved
. Mr Peter was walking home. He was robbed of his wallet

=>He was robbed of his wallet when Mr Peter was walking home.

. I don't have a pet. My brother doesn't allow me to have one

=>I don't have a pet because my brother doesn't allow me to have one.