Effect another player?

Well, a simple way to get you started would be using a 'Touched' function.

--script.Parent would be the blade (a part). Thus this script goes inside of it. But you can easily change that if you'd like.
debounce = false --To ensure that the humanoid does not lose all of their health instantly, we'll use debounce to yeild damaging.
script.Parent.Touched:connect(function(hit)--Fires when the blade is touched, and hit is the part that touched the blade.
    if debounce == true then return end --If debounce is true, then the function will not continue
    debounce = true --If debounce was false, then it will continue and make debounce true.
    if hit.Parent:FindFirstChild("Humanoid") then --Checks if the hit's parent contains a humanoid
        hit.Parent.Humanoid:TakeDamage(10) --Subtracts 10 health points from the humanoid. Change 10 to your desired damage.
    end --Ends if statement
    wait(1) --Yeilds for 1 second --this is how long the script will wait untill the function will be able to fire again.
    debounce = false --Now debounce is false, and the script can now fire again.
end) --Ends touched function

This is of course, one of the easiest functions to use for this sort of thing, and is good for beginners to use in order to progress.

I encourage you to build on to this script to your own liking, and learn on your own; we won't be able to provide for you all the time!

Hope this helped!