The openCAESAR project has been developed by NASA JPL to balance modeling rigor and agility. At the core of openCAESAR is the Ontological Modeling Language (OML), which supports two levels of modeling: vocabularies for defining domain-specific languages (DSLs), and descriptions for defining system models based on those languages. openCAESAR offers a framework for these languages, including editors, adapters, dependency management, semantic reasoning, and report generation. In this tutorial, participants will learn how the openCAESAR project and OML support modeling rigor and agility in systems engineering. This includes a) the development of vocabularies and descriptions in OML, b) how custom viewpoints can support modeling methodologies, b) how openCAESAR supports model federation and integration with release and dependency management, and c) how participants can set up automated model analysis with build scripts and CI/CD pipelines. We demonstrate these features in an open-source running example involving modeling a hypothetical Kepler-16b space mission, where participants will follow along with the tutorial as these features are shown. After this tutorial, Participants will be able to effectively use openCAESAR in an end-to-end fashion to define their own DSLs, use them to define system models, and run automated reasoning, verification, and reporting.