Are Concerns in Ruby on Rails replacement for service classes in MVC?

I am a newbie in Ruby on Rails. Coming from a C# and Java background, Ruby on Rails seems bizzare, yet interesting at the same time. It's almost like coming from a class-based object-oriented world to the prototyping concept of JavaScript, or even to a functional language.

Anyways, in a traditional C# or Java MVC application, I tend to keep my models and controllers as clean as possible, extracting the business logic into service classes. My models are just POCOs/POJOs (with some calculated fields and validation at most). And my controllers just process incoming requests (relying heavily on dependency injection) and then return a view or JSON.

Yet, I do not see any clear pattern in the RoR world. Some people tend to put all their business logic into controllers, some put it into models (with ActiveRecords, it kind of makes sense, although I don't like it).

And then there is the concept of Concerns. Are they the right place to extract my business logic, instead of using services? If yes, could you include an example of proper Concers use? I still struggle with the concept of modules (are they more of namespaces, or rather interfaces)? As said at the beginning, Ruby seems like a whole new galaxy to me.