You want to ask, "What is the difference between avocation and hobby?"
a hobby can be an avocation. a hobby is an activity one likes to do and does it willingly out of pleasure, and it makes them happy.
an avocation can make a person happy too, but the meaning is deeper in that an avocation is an activity someone is called to do in their life. It is part of who they are not just what they can do.
for example, a person who works a normal office job, but also is a volunteer as a coach for something like baseball camp or soccer for kids. They are working in an office to earn money and make a living, but their avocation is supporting children and inspiring them by being a coach. It gives that persons life a true meaning
hope this helps!