How to know if a tool hit a part ?

I want to know how to script something where if the tool touches a part ?

You can use the tool's handle to know if it's touched.

toolName.Handle.Touched:Connect(function(hit)
    if hit:IsA("Part") then
        if hit.Name ~= "Baseplate" then
            -- code here
        end
    end
end)

Handle is what makes up the tool, it's the part of union. Make sure to name it to to 'Handle'.