How would I make sparkles start in a players torso when the player touches a block?

Assuming you have a part named Button in Workspace, this should work:

game.Workspace.Button.Touched:connect(function(hit)
    if hit.Parent:FindFirstChild("Torso") then
        if not hit.Parent.Torso:FindFirstChild("Sparkles") then
            Instance.new("Sparkles", hit.Parent.Torso)
        end
    end
end)

Line 1: Connecting Touched event

Line 2: Checking if the Torso exists

Line 3: Checking if Sparkles already exist in the torso

Line 4: Adding sparkles