How to I give a attach something to player when they join?

So I'm Assuming that you want to Weld the Watch To The Player.

So First Off Make Sure to have the Watch in Replicated Storage oh and it can not be a union/mesh (I'm not sure how to weld those to the player yet) make sure its a group with normal bricks and have one part called Main so that you can recall to it later. but before we get into welding, make sure to have a dummy player arm so you can position the watch exactly how you want it to be. Once you are done with that put the watch back in Replicated Storage and insert a script to Server Script Service, Also Make sure to name your Model Something short for the script! Now its Scripting Time

This part is getting the Model or Model's From Replicated Storage

local rp = game.ReplicatedStorage
local LeftArm = rp:WaitForChild('LeftArm') --//This is just an Example Name for a Model
local LeftLeg = rp:WaitForChild('LeftLeg') --//This is just an Example Name for a Model
local RightArm = rp:WaitForChild('RightArm') --//This is just an Example Name for a Model
local RightLeg = rp:WaitForChild('RightLeg') --//This is just an Example Name for a Model
local Torso2 = rp:WaitForChild('Torso2') --//This is just an Example Name for a Model

Now Lets Hide The Body Part's When a Player Join's The Game! First Start with a 'Player Connected Function'

game.Players.PlayerAdded:connect(function(plr)
    plr.CharacterAdded:connect(function(char)

Then Add a 'char:WaitForChildAdded

        char:WaitForChild('Torso')
        char:WaitForChild('Left Leg')
        char:WaitForChild('Left Arm')
        char:WaitForChild('Right Leg')
        char:WaitForChild('Right Arm')

Now Let's Weld The Parts Together with the Watch

        --// Left Arm
        local ClonedLA = LeftArm:Clone()
        ClonedLA.Parent = char

        ClonedLA.Main.CFrame = char:WaitForChild('Left Arm').CFrame

        local Weld = Instance.new('ManualWeld')
        Weld.Part0 = ClonedLA.Main      
        Weld.Part1 = char:WaitForChild('Left Arm')
        Weld.C0 = ClonedLA.Main.CFrame:inverse() * char:WaitForChild('Left Arm').CFrame
        Weld.Parent = char:WaitForChild('Left Arm')

    end)
end)

To Be honest i kinda feel like i did the entire script for you XD but i don't mind i love helping people out!

Best thing to do is to make the watch an accessory or a gear that the character can use if it had a script. Otherwise, u could weld the watch model onto your character by clicking run, and then welding the watch onto your spawned character by clicking the model in the replicated storage and moving it onto the part called TheArcticTerminal. This is the best I can do, otherwise look up the answer on youtube, or maybe in group script assistance. If this answer helped you solve your question, please click accept below this answer to eliminate space upon other questions. Good luck with your watch!!