This is a set phrase used to acknowledge someone's efforts and to show your appreciation for work they did. In polite situations you add desu to the end. The casual form of this is otsukare. This phrase can mean any of the following in English,
● You must be tired (from working hard)
● Thank you for your hard work
● I appreciate your hardships
● You worked hard
This phrase can be used to dismiss someone from their job or duty. It can also be used to say goodbye/thank you when you leave school, a meeting or work.
This phrase literally means something close to a hard worker. It is used in pretty much the same way as otsukaresama but it's used less frequently. Generally this phrase is used more for thanking someone of lower status for doing a task for you.