The Option Chain display shows call options to the left and put options to the right of the central strike column.
Clicking a single strike will close the Option Chain window and populates the Order Entry panel with the chosen option leg.
Use the Order Entry panel to define the quantity of options to trade. Choose the right order type from the dropdown menu.
Our order is ready to review. Click the Submit button to generate an Order Confirmation. When you have reviewed the details, click Transmit.
Source: (IBKR, 2023, PRACTICAL USAGE – BEAR MARKET – LONG PUT, https://ibkrcampus.com/trading-lessons/practical-usage-bear-market-long-put/ )