Instagram marketing involves both paid and unpaid strategies. Paid strategies include advertising and influencer marketing, while unpaid strategies are organic posts, stories, comments, and engaging with other users' content. The goal is typically to sell products/services, gain followers/interaction, develop relationships, and improve brand reputation. Instagram's algorithm calculates the likelihood someone will interact with a post based on factors like post information, the poster, the user's activity, and interaction history to determine the order posts appear in the feed.