A boosted post is when you put money behind an existing organic post on your page to get it seen by more people. You can set your budget and basic demographics, such as the age and area of the people you want your post to be seen by.
Facebook, Instagram and Messenger Ads are built in the Facebook’s Ads platform itself, requiring you to choose a campaign type, add copy and imagery, alter your audience and more. The Facebook Ads platform learns about your audience and gives you better results over time.
The main difference between boosted posts and Facebook Ads is the level of intelligence and features you can put behind the ad campaign to ensure it goes to who you want with the right messaging. Boosted posts are great for short-term boosts of views of a specific post, but Facebook Ads are what will grow your business.