If you've defined one or more sector frames in your model, you can choose to run selected sectors rather than the entire model. This lets you run simulations for functionally-related building blocks, so you can observe their behavior in isolation.
Navigate to the root module by clicking on the button in the Mode toolbar (if it's not visible, you're already in the root module).
Double-click an empty part of the model to open Model Preferences, and click on the Partial Simulation tab to access Partial Simulation Setup.
Select the sectors you want to run:
Note: Sectors whose names are grayed out can't run, because they're not fully defined (don't have all variables defined), or have errors.
Run the model from the Model menu or the Run Toolbar. Depending on your selections, only a subset of the model will run.