Pick the legs in the chain
Click a bid to sell that contract and an ask to buy it; click again for more contracts. Up to four legs on one expiry. The structure's profit and loss at expiry, its greeks and the buying power it ties up are worked out as you go. Nothing is sent from here: Use this in the trade ticket fills in the ticket, where you check it and send it with a recent authenticator code.
No host is publishing an option chain right now. Start a core host with --nats on a live feed (see the board's option chain widget), then reload this page.
Your structure
No legs yet. Click a bid or an ask above.
The ticket opens with these legs and the limit filled in; you check it there.