Online advertising platforms target users by employing sophisticated methods that analyze user data to serve personalized ads. These platforms utilize cookies, browsing history, and demographic information to create user profiles. This enables the delivery of relevant advertisements based on individual preferences and behaviors. Additionally, platforms like Google and Facebook use machine learning algorithms to optimize ad placements, maximizing engagement and conversion rates. By employing retargeting strategies, advertisers can re-engage users who have previously interacted with a brand, further increasing the effectiveness of their advertising campaigns.