Im thinking about making a [blank] type of game and I want to know if its possible to make a pause system. An example would be I press “p” and everything and everyone, all the guis, EVERYTHING freezes and the game just stops playing, but then I unpause and the game starts working again. Is it possible to do that? If so I’d like know how to do it please. I have no clue how I would begin scripting it. Would there be like an api or something for it?
Thanks 
Ex:
The only way you would be able to do it is make code everything yourself to act a certain way while the game is “Paused” which would give it the effect of being paused.
This “pause” system would only have to be done locally as it would otherwise freeze everyone else in the server in time, and I don’t think players would want that .
You could use some sort of function that just sets all moving part’s base velocity to 0 or another idea would be to clone every thing visible by the player, i.e the Workspace’s descendants to somewhere else and change the player’s camera locally, to face that area upon a certain key being clicked, using
UserInputService binding a key with the function.
You could make a function that will pause any action of the actual game, but you would need to make how the pause function will act and what will it do, here is a not tested code that might help you:
function Pause()
--[[ Lighting Behaviour ]]--
game.Lighting.Ambient.Color = -- whatever ambient
--[[ Humanoid Behaviour ]]--
local Players = game:GetService("Players")
local Player = Players.LocalPlayer
local char = Player.Character
local Humanoid = char:WaitForChild("Humanoid")
Humanoid.WalkSpeed = 0
--[[ UI Behaviour ]]--
local PlayerGui = Player:FindFirstChild("PlayerGui")
local PauseGui = PlayerGui:FindFirstChild("Pause")
PauseGui.Enabled = true
endits a client game so there would be 1 player also thank you!
You might want to use some form of module scripts / _G variables when you do this, Because:
For example, if you’re running a loop you can do this:
while wait() do
if _G.Paused == false then
--execute code here if game is NOT paused, else if it is, it won't do anything
end
end
This will also apply to OnClientEvent functions so that the player doesnt receive updates from the server either.
You may want to log the player’s velocity also before you “pause” the game so that when you unpause, you set the player’s velocity back to the logged velocity making the player move again.
Theat’s just a few more things to consider when “pausing” a game
Think about this.
Why is Roblox not pausable? Maybe because other clients are moving even when you press escape? Maybe because someone can hurt you while you ‘pause’ the game?
Hence, do this from the client then. Make the player invincible (might be abusable tho’), (if you want, freeze other players, or everything, in the client, since it will appear as other players aren’t moving then)
My opinion tho, would be to use a Menu that covers the whole screen, or a menu that changes the camera subject to something else that also shows a Menu.
I guess that will be it.
This is all possible with the use of _G as mentioned by @InternallyAmplified.
In the scripts that you want to pause you can do
repeat wait() until _G.Paused == false
And in your Pause Script you can set the value by doing:
function Pause()
if not _G.Paused then
_G.Paused = true
elseif _G.Paused then
_G.Paused = false
end
end
Hope this helped you out 
Yes, you can use _G’s but it’s unstable. use ModuleScripts instead.
You also can adjust variables inside it.