Need help with :format()

I need help with how this works and what it is.

local Label = script.Parent.Label

Label.Text = ("Hello there, %s!"):format(player.Name)

What is, format?? And how does % work?

Format is putting a string that can be formatted as accordingly to specifiers:

Since "Hello there, %s!", is a string and uses the %s specifier for strings only. The string uses a function called format. Arguments included will replace the %s with whatever string that comes first.

Most of the time string.format is used to replace strings. I think something else can be done.
Instead of:

String1 .. String2

It can be used:

local String1 = "Hello, %s"

Like what you did, the last part %s changes depending on what you will do.
It is very useful for very long strings.

local String = "Hello, I am %s and I have come to explain about %s!"

local User, ToExplain = "SOTR654", "string.format"
local String = "Hello, I am " .. User .. " and I have come to explain about " .. ToExplain .. "!"