Log in from the main page via Facebook, Gmail or by creating account with username and password.
You will be redirected to the task list (or click Problems link in the top menu to get there), looking like this:
Here you see how your list will look after you solve some problems.
Choose some unsolved task by clicking its name. For example, let us try solving the Vowel Count task. You will be redirected to the page with problem statement.
Go to Step 2 to learn about problem statement and submitting solution.