How to make this create an explosion?

Whatever the paintball hits, it creates an explosion that does 25-1000 damage depending on if it's a direct hit or splash damage. Anyone help? By the way, blast pressure is 0, and blast radius I will determine.

ball = script.Parent
damage = 25



function onTouched(hit)
	local humanoid = hit.Parent:findFirstChild("Zombie")

	

	if humanoid ~= nil then
		tagHumanoid(humanoid)
		humanoid.Health = humanoid.Health - damage
		wait(2)
		untagHumanoid(humanoid)
	end

	connection:disconnect()
	ball.Parent = nil
end

function tagHumanoid(humanoid)
	-- todo: make tag expire
	local tag = ball:findFirstChild("creator")
	if tag ~= nil then
		local new_tag = tag:clone()
		new_tag.Parent = humanoid
	end
end


function untagHumanoid(humanoid)
	if humanoid ~= nil then
		local tag = humanoid:findFirstChild("creator")
		if tag ~= nil then
			tag.Parent = nil
		end
	end
end

connection = ball.Touched:connect(onTouched)

wait(0.8)
ball.Parent = nil

Go to this link: Explosion Damage. It will give you everything you need. Hope this helped!

Well this would be how to create the explosion. I'm kinda lost on how to make the damage part.

ball = script.Parent
damage = 25



function onTouched(hit)
    local humanoid = hit.Parent:findFirstChild("Zombie")
    E=Instance.new("Explosion",game.Workspace)
    E.Position=humanoid.Position
    E.BlastPressure=0
    E.BlastRadius= --Enter what you want here.

    if humanoid ~= nil then
        tagHumanoid(humanoid)
        humanoid.Health = humanoid.Health - damage
        wait(2)
        untagHumanoid(humanoid)
    end

    connection:disconnect()
    ball.Parent = nil
end

function tagHumanoid(humanoid)
    -- todo: make tag expire
    local tag = ball:findFirstChild("creator")
    if tag ~= nil then
        local new_tag = tag:clone()
        new_tag.Parent = humanoid
    end
end


function untagHumanoid(humanoid)
    if humanoid ~= nil then
        local tag = humanoid:findFirstChild("creator")
        if tag ~= nil then
            tag.Parent = nil
        end
    end
end
	
connection = ball.Touched:connect(onTouched)

wait(0.8)
ball.Parent = nil