In the Earth Observation (EO) domain, data analysis ranges from simple image processing tasks like dilation to complex workflows involving Machine Learning (ML) and Deep Learning (DL). While openEO provides numerous features and functions for data analysis, but given the broad scope of the field, not all potential needs are covered out of the box. To address this, openEO supports User-Defined Functions (UDFs). These UDFs are implemented as standard Python scripts using libraries such as Xarray or Numpy. They allow users to implement custom workflows tailored to specific research requirements. Thus, in this course, we offer a high-level introduction to openEO with a focus on UDFs and include an example of an advanced EO workflow that applies this concept in practice.