Implementing update_user_meta

I am busy making a page in which users can choose between a variety of programs and subscribe to one.

Once the users have subscribed to a program, his/her choice has to be saved in the database. Later when the user visits the webpage again, he/she can see the programs they have subscribed to. I am trying to save the programs the user has subscribed to with update_user_meta. Later I want to view them on the download page with the get_user_meta.

My question: I do not know how to implement update_user_meta in my code. How can I do that?

My code: