Follow the tasks on the main page, they will guide you to create a user and log in whenever you need.
After logging in you can create your own tasks, to do so click on the + sign to create a new task. Then fill in the fields, only the description is optional.
Yes, you can use markdown on the description field, we support a nice set of extensions, just some:
Can be entered by typing:
Name | Age --------|------ Bob | 27 Alice | 23
stroked through text using tildes:
There is a small link, edit task, below the date when you are seeing a task.
See https://daringfireball.net/projects/markdown/ to learn more.