Go to your dashboard and find the section "Create worker", Type in a username and password and click create.
Download and install GUIMiner from http://forum.bitcoin.org/index.php?topic=3878.0 or start_miner from BitmonMe
Once installed, configure it as shown below with the worker credentials you created in your dashboard.
Click Start mining! You are now solving blocks on gbyte.dk, and can check your statistics here. Or in your dashboard.
Depending on our hash rate, it could be a matter of hours or days before gbyte.dk gets a block. But if you provided hashing power for solving the block, you will receive your part of the solved block.
To receive earnings from gbyte.dk install the Bitcoin application from http://www.bitcoin.org/
Copy your Bitcoin address to clipboard, add it in your dashboard and click Save. When you have a balance of minimum 0.01 BTC you can click Instant payout and the amount will show up in your Bitcoin application.