Your 'Used Margin’ section would be used in either of these two scenarios:
From your total 'Available to Trade' balance, when an amount of funds is used for trading, this amount will be shown in 'Used Margin’. This is denoted as a positive amount. The possible scenario when this may happen is:
You buy Stock in the Equity Delivery segment.
You buy or short sell a Stock in the Equity Intraday segment.
You buy or short sell a Derivatives (Futures & Options) contract in Intraday or Delivery.
You carry forward an open position to the next trading day for either a Futures contract or an Options contract (on the short side only).
Whenever you successfully sell a Delivery position, an amount will be receivable by you, and this amount will be shown in 'Used Margin'. This will be denoted as a negative amount. The possible scenarios when this may happen are:
You successfully sell a Stock in the Equity Delivery segment (from your Demat account).
You sell an open position (on the buy-side) in the Options segment.