Yes, whereas is a conjunction, specifically a subordinating one. It fits when your second clause contrasts with the first: I like tea, whereas she prefers coffee.
Generally, you'll want a comma before whereas when it starts your second clause. That's the normal setup: The old office had no windows, whereas the new one gets light all day.
You can also let whereas open the whole sentence, in which case the comma goes after its clause: Whereas the first draft ran long, the final version stayed under ten pages. If you'd rather keep your main statement first, the usual setup is to let whereas start the second clause with a comma before it: The final version stayed under ten pages, whereas the first draft ran long. Both placements are standard; the choice is mostly about which statement you want to land on.
When your second clause contrasts with the first and whereas starts it, keep whereas mid-sentence with a comma before it: Sales rose in June, whereas July brought a sharp drop.
If the contrast should lead your sentence, put whereas at the very start: Whereas the pilot group finished early, the main team needed two extra weeks.
Whereas is a subordinating conjunction, so it always introduces a clause and can never end a sentence. If your contrast clause would fall last, move it after whereas instead: not He jogs daily, whereas. but He jogs daily, whereas his neighbor barely moves.
Whereas needs a second contrasting clause to introduce, so use it only when you actually have one to state. If one clause already says enough, you don't need whereas at all: The report is final. stands on its own, while The report is final, whereas the draft still needs revision. gives the connector a real clause to introduce.