I'm not sure if you're just asking about how to get option trading permission or how to enter an order.
If A: log into account management, select trading permissions and tick off US stocks and US options. then once approved, select Data Subscriptions, the US Option exchanges/US data package.
If B: you can do a few different things which I suggest you try from the demo.
1. Enter an option the same a a future. Ie. IBM <enter> then chose option, year month strikem exchange (choose SMART). the strike appears on the screen and you trade it just like the future.
2. You create an option chain page. on the page with the chain all the strikes apprear and you trade.
You can also trade combos/spreads. instead of chosing OPTION, choose COMB. A box appears and you can choose the strategy via a series of pop up boxes.
There is also an option analytics package which is available.
for the above, i'll repeat you should try this on the demo and also make sure you read the manual (under help/system guides/TWS user guide) for specific info on configurations of the option chains, exercise instructions, analytics, etc).