Niels's answer is good and I'd like to add a bit more,
1. The guy who is standing over there is my boss.
--> あそこに立っている人は私の上司[じょうし]です。
The word order would be "over there, standing, the guy, my boss, is".
2. The flower that is blooming is Sakura Tree
咲いている花はさくらです。
The word order would be "is blooming, the flower, Sakura (tree), is".
*Please remember that word orders might be changed depending on the sentence / context.
I think practicing a lot is good to understand the construction. I hope this helps you.