It is fairly complex, there are a series of tutorials but the learning curve is fairly steep. These three apply to the latest version of Fritzing, most of the rest are for older versions (pre parts editor):
I can do that easily enough (it is usually the best bet if you are new to part making), or perhaps there is one somehwhere, but I need the data sheet or at least a part number that will lead to the data sheet for the switch you want to know what it needs to look like.
Parts editor was not completed when development stopped in 2016, thus can only add new connectors in the fzp file, not the underlying svg files (I’m not even sure it can add connectors new connectors at all, but I am not all that familiar with parts editor either.) Thus you need to use a svg editor such as Inkscape to modify the svg files (which implies you know the format to do that which is poorly documented.) That is part of what makes part creation difficult (and the lack of documentation doesn’t help.) I generally find parts editor not worth the effort and just modify the underlying files directly, but that requires knowing what the files need to look like.