What it means
A call to action names the action and makes it easy. It is the button, the line above the button, and the sentence at the end of the post. Good ones say what happens next and what it will cost the reader in effort.
Why it matters to a small business
Small businesses write beautiful posts that end with nothing, and the reader nods and scrolls on. The failure is not persuasion, it is instruction. Telling somebody exactly what to do, in words they would use themselves, converts better than another paragraph about how much you care.
The bit people get wrong
Learn more and Find out more are not calls to action, they are shrugs. They commit the reader to nothing and tell them nothing about what is on the other side. Book a table, Get a price in 24 hours and See this week's menu all name the thing.