The Calibration Castle tests the following:

Extrusion quality
Bridging
Overhangs
Retraction
Accuracy
Cooling performance

It's recommended to print the model at 0.15 mm layer height and only add support on the left side (the support test feature)

Before printing, you should calibrate your extruder steps and flow rate.

https://3dprintbeginner.com/extruder-calibration-guide/

https://3dprintbeginner.com/flow-rate-calibration/