?Can someone help explain these things:

I never got how people used ipairs, pairs, or #. It's like... I just don't get it.

ipairs and pairs are simply built in functions that iterate through arrays/tables. They are there for convenience so you don't have to write your own. These are used in generic for loops.

Usage example:

local array = {
	[index] = value,
	[2] = "b",
	["Apple"] = "Banana"
}

for index, value in ipairs(array) do
	print(index, value)
end

--[[Output
	index output
	2 b
	Apple Banana
--]]

# is used to retrieve the number of items in an array/table. These are commonly used in basic for loops.

Usage Example:

local array = {1, "Apple", game.Workspace}

for i = 1, #array do
	print(array[i])
end

--[[Output
	1
	Apple
	Workspace
--]]