Financial markets have changed a lot in the past 20 years. This thesis looks at three main issues: how technology affects trading, how exchange-traded funds (ETFs) compete, and why trading happens more at the end of the day. The research shows that high trading activity doesn't always mean something bad is happening. It also explains why some ETFs with high fees can still do well. The study suggests that trying to limit trading activity could hurt how easily people can buy and sell stocks.