The easiest way is to add a security or ticker symbol to your Watchlist and right click on the symbol to choose Trade > Order Ticket (or Trade > Order Entry). Select Sell to place a sell order. You will then have the opportunity to configure your order parameters.
You can refer to this page for selling a product short.
Note
- There is an abundance of educational material on the website including a short video and recorded webinar to cover the TWS basics.