How would I make the Character get faster as it moves?

local hum = script.Parent:WaitForChild("Humanoid")
local torso = nil

--check rig type
if hum.RigType == "R6" then
    torso = script.Parent.Torso
else
    torso = script.Parent.UpperTorso
end

while wait() do --put a number in the () if you want to slow down speed incerasing
    if torso.Velocity.Magnitude > 1 then
        hum.WalkSpeed = hum.WalkSpeed + 0.1 --this is how the walkspeed incerases
    else
        hum.WalkSpeed = 16 --default walkspeed
    end
end

Put this into StarterCharacterScripts. Works with R6 and R15.

You should indeed use loops and use increments, It isn't done completely in a loop because it would add to the speed when the player isn't moving, script is below, the explenation is too, if you need some more explanation, feel free to ask (btw mark this as answered please xD)

Script needs to be in workspace

Increment = 1 -- It will become this much faster every time
DelayT = 0.1 -- It will wait this time before it starts the loop again
defSpeed = 5 -- Starterspeed, this number will change trough the loop
maxSpeed = 100 -- If you don't want this set it to 99999999999999999999999 or something like that xD
Speed = defSpeed
plrWalking = false

game.Players.PlayerAdded:connect(function(player) 
    player.CharacterAdded:connect(function(char)
        player.Character.Humanoid.Running:connect(function(speed)
            if speed > 0 then -- player isn't standing still
                plrWalking = true
            else
                plrWalking = false
            end
        end)
    end)
end)

while wait(DelayT) do

    for index, player in pairs(game.Players:GetPlayers()) do
        char = player.Character or player.CharacterAdded:wait()
        hum = char:WaitForChild("Humanoid")
        if hum and plrWalking and Speed < maxSpeed then -- if humanoid and player is walking
            print("plr is running")
            Speed = Speed + Increment
            hum.WalkSpeed = Speed -- increasing speed
        elseif not plrWalking then
            Speed = defSpeed
            hum.WalkSpeed = defSpeed -- reset speed when stopped
        end
    end
end