Depends where the moss is, you'll need a lawn moss treatment for grass, otherwise buy a liquid mosskiller, Murphy used to make one, don't know if its still available.
As for ground elder, you need a two pronged approach - treat with glyphosate when its growing strongly, wait a week and treat again, wait another week and then dig out every piece of it you can find, including all the roots. The glyphosate doesn't usually kill it off completely, even if it looks like it has, but what it does do is kill off the very fine, hairlike roots which are impossible to extract otherwise.