Investing in securities involves analyzing and selecting the right ones to make a profit. There are different strategies like active, balanced, or passive investing. The goal is to create a portfolio that makes the most profit with the least risk. Managers use tools like Sharpe’s index and Treynor’s index to measure how well the portfolio is doing. They adjust the portfolio to make sure it's as efficient as possible. By using these tools, managers can create and maintain an optimal investment portfolio that meets the preferences of investors in terms of profit and risk.