How do i make a block that push's me back when i touch it?

Alright man. If you've ever seen a killbrick you should be able to use Itzlewis' answer to solve your problem. But I'll give you how to get the player from the server side.

function onTouch(hit) -- hit is the part that touched
	local hum = hit.Parent.Humanoid -- checks for a humanoid. if not found, returns nil
	if hum then -- makes sure the humanoid was found
		local c = hum.Parent -- this is also the Player's character
		local BV = Instance.new("BodyVelocity", PARTYOUWANT) -- replace "PartYouWant" with the proper parent, like Itzlewis said. I think you want c.HumanoidRootPart, but idk.
		BV.maxForce = Vector3.new(25000,25000,25000)	  -- it's just your code after this                  
		BV.Velocity = c.HumanoidRootPart.CFrame.lookVector*40
	        game.Debris:AddItem(BV,0.5)
                BV.Velocity = BV.Velocity + Vector3.new(0,15,0)
	end
end

script.parent.Touched:connect(onTouch)	

And yeah that's it. You should be able to get the player from the server side because touched gives the touching part automatically as the first parameter. If you don't know what i mean by that, i highly recommend you look at this: https://developer.roblox.com/en-us/api-reference/event/BasePart/Touched

Thank you. Any problems you can reach out to me via discord (BlobMaster#8156) or you can message me on roblox. pls only message me if you have a problem relating to this question, though the code i gave you should fill your needs. Till next time.