Use ParaView to create your first Catalyst script. Load a result file from your simulation code, add a slice, then a VTPC extractor. Use file → save catalyst state. You will see that in the created python file, the file reader has been exported. That file reader has a registrationName=“something”. Replace the registration name content by the channel name you used on the simulation code side. Catalyst will use the Conduit channel instead of reading the file as the start of the pipeline.
Make sure you go through all the docs, as it can be a bit tricky to get started.
https://catalyst-in-situ.readthedocs.io/en/latest/index.html