This tab is used to configure the details of the target server for the attack. The required options are:
The easiest way to configure these details is to select the request you want to attack anywhere within Burp, and choose the "Send to Intruder" option on the context menu. This will send the selected request to a new tab in Intruder, and will automatically populate the Target and Positions tabs.
Get help from other users, at the Burp Suite User Forum: