WalkSpeed is a property that describes how quickly a Humanoid is able to walk, in studs per second. This property defaults to 16, so a Roblox Player.Charactercan move approximately 16 studs in any direction each second by default.
I will provide two examples for you to understand on how to do this.
Go to StarterPlayer in the explorer. (view tab->explorer)
In the properties, (view tab->properties) look for the WalkSpeed property. It should have a default value of 16.
You can edit this number to be any number you want.
PlayedAdded and CharacterAdded are events.
PlayedAdded runs when the player joins the game CharacterAdded runs when the player's character loads into game.
Inside of character added, we change the players walkspeed. this means whenever the player's character loads, their walkspeed will be changed to 'newWalkspeed' .
local newWalkspeed = 10 -- You can change this value to any number you want game.Players.PlayedAdded:Connect(function(player) player.CharacterAdded:Connect(function(character) character:WaitForChild("Humanoid").WalkSpeed = newWalkspeed end) end)