How to teleport because of value to random spawn?

Get the number of parts in the model you could do that and get a random number by doing:

local randomNum = math.random(#modelName)

Say if your model has 50 parts, this will generate a random number between 0 and 50, now to get the player onto the part, you should give the parts a specific name that way you can teleport them like so:

p2.Character.Torso.CFrame = modelName["specificName"..tostring(randomNum)].CFrame

Please note, in the wiki they say that this will not give out a random number for the reason that it will take the previous number into account. So in order to get a truly random number, you will have to set the seed. In the end, it should be something like so:

math.randomseed(tick())
local randomNum = math.random(#modelName)
p2.Character.Torso.CFrame = modelName["specificName"..tostring(randomNum)].CFrame

It could not work, since i have not tested it. But if you have any problems, feel free to comment.

[EDIT]

You want to get all the players and put each on a random part. Easy, just use

for _,player in pairs(game.Players:GetChildren()) do
    local findPlayerInWork = game.Workspace:FindFirstChild(player.Name)
    if findPlayerInWork then
        sendPlayerToPart(findPlayerWork)
    end
end
function sendPlayerToPart(plr)
    math.randomseed(tick())
    local randomNum = math.random(#modelName)
    plr.Character.Torso.CFrame = modelName["specificName"..tostring(randomNum)].CFrame
end

Again, not sure if it works i haven't tested it in Roblox Studio. But i think it should work. :)