First, head to http://188.8.131.52/register to sign up. You'll need to provide a username and password- make sure you don't forget these as you'll need them to sign in.
Then you can go to http://184.108.40.206/ and sign in to start making submissions.
Each of the 6 problems has an entry on the right. Click the "Submissions" link below the appropriate question to get to the question page. From here, you can upload your solution and have it evaluated by the server. Within a minute, you should get a score from the system; each passed test case gets you 10 points, and the test cases are progressively harder.
You can submit solutions as many times as you like, but only the most recently submitted solution will count towards your final score.