math.random How does it work?

The math.random function returns random numbers based on the given arguments. It can work in 3 ways:

No arguments:

print(math.random())  -- No arguments, and returns a random number between 0 and 1 (0.1,0.2,0.3, ect)

One argument:

print(math.random(5)) -- Prints a random number between 1 and 5

Two arguments

print(math.random(5,10)) -- Prints a random number between 5 and 10

This algorithm can be used in a lot of useful ways, especially when creating a game based off random events. But, this function only returns a numerical value. Which means you have to base your random events off the numerical value it returns.

I'll give an example in the form of your scenario:

local Maps = game:GetService("ServerStorage").Maps:GetChildren()
local RandomMap = Maps[math.random(#Maps)]  

-- "#Maps" is the numerical representation of how many maps there are.
-- So we can get a random number between 1, and #Maps

GetChildren() returns a table of children from the parent it's called on. You can index this table with a number. In this case, i indexed it with a random number. Giving me a random key (map).

Edit:

And yes, you can use this with various types of Colors, such as creating a random BrickColor, or creating a random Color3 color (for Guis, Effects, and anything that has a Color or Color3 property). Though these methods don't involve using the "random" function from the "math" table.

Here are some examples:

Using BrickColor.Random():

local p = Instance.new("Part",workspace)

local RandomBrickColor = BrickColor.Random()  -- Random brick color

p.BrickColor = RandomBrickColor

You can also convert this random brick color to a Color3 value, so it can apply to any object that has a Color3 property:

-- Assuming this script is inside a GUI with a color value

local RandomColor3 = BrickColor.Random().Color  -- Using .Color will convert it to Color3

script.Parent.BackgroundColor3 = RandomColor3

Though, most people tend to stick to the method of calling math.random 3 times in place of the RGB values of Color3 like this:

-- Assuming this script is inside a GUI with a color value

local RandomColor3 = Color3.new(math.random(), math.random(), math.random())

script.Parent.BackgroundColor3 = RandomColor3

-- Since Color3's RGB arguments are based on a scale of 0 to 1, this method will return a random Color3 value.

But either way works, so it all depends on what you like best. Hope this helped.