MarkF from Azure team. The actors in Dapr are based on the same virtual actor concept that Orleans has, meaning that they are activated when called and eventually garbage collected. If you are familiar with Orleans, Dapr actors will be familiar. The difference with Dapr is that because it is programming language agnostic with an http/gRPC API the actors can be called from any language (although there are also friendly language SDKs on top).
Creating a new actor follows a local call like http://localhost:3500/v1.0/actors/<actorType>/<actorId>/meth...
for example http://localhost:3500/v1.0/actors/myactor/50/method/getData to call the getData method on myactor with id=50