Help me figure the line of motion in the entity animation code

Hello! 
Are there people here who understand coding? I want to start learning to code entity animations. But I cannot understand the meaning of these lines. And I would like to ask those who know the answers to my questions. Namely - What does func mean and what role does it play? How can I calculate the OpenGL coordinates for the movement? (I have a Geckolib animation in the code of which all the necessary coordinates for the movements are written, but I cannot figure out how to correctly transfer these coordinates to the OpenGL coordinates) And also how to specify the desired timeline for the movement? (I sanitize a second)
If someone knows a good guide that can help me, please share.