I start with generating tags.

  exctags --exclude=TAGS --exclude=TAGS.NEW --append -R -f TAGS.NEW --sort=yes  && mv TAGS.NEW TAGS

My editor (vim) has native support for quickly jumping from a use to definition via this TAGS index. History is preserved (i.e., there is a "back" button), so you can quickly dive through 5 layers of API and back out to understand where a value went. It is quite useful for starting with what you know and following it to the surprising behavior, without executing the code.