looks self explainatory , unplug sparkplug wire , plug the gadget to sparkplug and push wire onto the sparkplug shaped tip , start it up , if see spark its workin

dont believe its for full time use just diagnostics when having starting problems , I normally test if I have spark by sticking 1 finger into plug wire and another (same hand) onto the plug itself and cranking it :o zap zap zap zap yup its got spark