You have already used fmt.Println. It prints its arguments with a
space between each one and a newline at the end, and gives you no
control over the layout:
fmt.Println("port:", 8080) // port: 8080
fmt.Printf is the one to reach for when you want the output laid out
exactly. It takes a format string with placeholders, called verbs, and
fills them in from the arguments that follow:
fmt.Printf("port: %d\n", 8080) // port: 8080
The %d is a verb that means "put an integer here". One difference to
remember: Printf does not add a newline for you, so you write the
\n yourself at the end of the format string.
When the exact shape of a line matters, Printf is the tool.