What is difference between Tasklist and My Tasks?

Timeline and My Tasks are both used to manage your Tasks. 

Every Project has its Tasks in a Tasklist format, so that they can be organized. But if you'd like to see Tasks from multiple projects at one place, My Tasks will give you that option.

Also, if you want to check Tasks from a single Project in My Tasks section, you can use filter to select that project, and check those very Project Tasks in a list view.