Standard 1.4x teleconverter increases the effective focal length of your lens by 1.4x, and reduces the aperture by 1 f-stop.
For those of you who haven’t used teleconverters, please be aware: “there is no free lunch”. You will get a longer focal length, but at the cost of a bit of sharpness. Teleconverters generally work well with professional grade f/2.8 telephoto lenses. They do not work well with consumer grade f/5.6 zooms.