How do I choose one player and give them a sword?

Here are some of the basics. You'll have to edit some things in order for it to work, but this is what it would look like for the most part.

function ChoosePlayer() -- declare function
    local players = Game:GetService("Players"):GetPlayers() -- player list
    local plr = players[math.random(#players)] -- random player
    local hum = plr.Character:WaitForChild("Humanoid") -- declare variable for Humanoid
    Game:GetService("ServerStorage"):FindFirstChild("Sword"):Clone().Parent = plr:FindFirstChild("Backpack") -- give sword
    hum.MaxHealth = 200
    hum.Health = (hum.Health / 100) * hum.MaxHealth -- heal the character proportionally
    hum.WalkSpeed = 32 -- change walkspeed
    plr.Character:MoveTo(Vector3.new(0, 0, 0)) -- teleport
    return plr
end

local chosenPlr = ChoosePlayer() -- call function
local msg = Instance.new("Message", Workspace)
msg.Text = chosenPlr.Name .. " was chosen!"
Game:GetService("Debris"):AddItem(msg, 3)