How to insert and remove items from all players inventories?

Hi there! If you are wanting to remove every player's items on a game, you would have to use a for loop, which would loop through

game.Players:GetChildren()--This returns a table of ALL the players in the game

Here is an example script for removing all of the players items:

local players = game.Players:GetPlayers()
for i,v in pairs(players) do--the variable "v" is equal to the target player
    v.Backpack:ClearAllChildren()--This removes everything in the targetted players backpack
end

To give everyone an item, you would need to define the object you want to give, and then use a for loop again:

local players = game.Players:GetPlayers()
local object = definethis
for i,v in pairs(players) do
    local newObj = object:Clone()
    newObj.Parent = v.Backpack
end

Hope this helped!