Form
Clause 1, + but / while / whereas + Clause 2
(To show a direct difference between two parallel ideas)
I like coffee, but my brother prefers tea.
He is very outgoing, while his sister is quite shy.
Meanings
Comparing two different but expected facts.
We use words like but, while, and whereas to simply state two different pieces of information. There is no surprise.
Fact 1: She is rich.
Fact 2: Her brother is poor.
→ She is rich, whereas her brother is poor.