Your strategy is essentially one or more stock screeners that a stock must pass. It can also be a set of individual stocks that you entered so you can track and get alerts when they pass a certain stock screener or trading model.
As new stocks pass your strategy you will be alerted to buy. If a stock once passed your strategy but no longer does, you will be alerted to sell.
You can also add stock screeners to your blacklist. These screeners have criteria that you do not want any of your stocks to pass. If they pass you will be alerted to sell.