Cloud infrastructure, as we all know, is divided into IaaS, PaaS, and SaaS. Managed services fall under PaaS and SaaS services. So, the major managed services in GCP are Dataproc, Dataflow, and BigQuery.
Get a complete understanding of Dataproc, Dataflow, and BigQuery; perform some hands-on work and you should get a clear idea about it.
Other services that you should be aware of also include Cloud Datalab and Google Data Studio.