Purpose of various steam locomotive parts

In my further endeavors to learn how steam locomotives work, I would appreciate it a great deal of some of the more knowledgable visitors of this site could anwer the following questions.
What is a blowdown and what is it used for?
What type of tools and oil cans would be commonly found on a typical narrow gauge steam locomotive?
What types of repairs are enginemen commonly expected to be able to make while out on the road?
Does all the electricity "generated" by the generator used to run the head light, cab light, etc. or is there a battery where excess electricity is stored? or is the excess, if any somehow just "vented" for a lack of a better word?
Thanks for answering.