Look at http://scala-exercises.47deg.com/ to begin.
A good thing could be to buy the `Functional programming in Scala`.
You’ll learn Scala and FP and it’s a great book.
For me, as you can code in an imperative form with Scala, you could be immediately productive with.
Once you’ll learn FP things, you’ll can rewrite/improve your imperative code with these FP things.