Now we can add the algorithms to derive the catchment.
1. Add the SAGA Upslope area algorithm from the Algorithms panel.
2. In the Upslope area dialogue change the Description to Delineate catchment. Link the Target X coordinate to X Coordinate Outlet and the Target Y coordinate to Y Coordinate Outlet. Use the Filled DEM input as Filled DEM. For Method use D8 and leave other settings as default.
3. Click OK.
In the next step we're going to polygonize this catchment raster layer.