An Iceberg Order hides part of the order size from the market. Only a small portion (the display size) is visible in the order book at any one time.

When the visible part is filled, the system automatically refreshes it with the next portion until the total order is completed.

Click the black MX button in the Trader Ladder, set your lot size, then set your size that is shown on the Market.

Then click the bid or offer price you want.