I have no idea where you are getting stuck so I’ll just give you the links I used :-
http://fritzing.org/learning/tutorials/creating-custom-parts/
http://fritzing.org/fritzings-graphic-standards/#download
http://fritzing.org/learning/tutorials/creating-custom-parts/providing-part-graphics/
https://learn.sparkfun.com/tutorials/make-your-own-fritzing-parts
http://www.inkscapeforum.com/viewtopic.php?f=5&t=20327&p=76831#p76831
http://www.inkscapeforum.com/viewtopic.php?f=5&t=20458&p=77166#p77166