This section of the ECB online-help is displayed automatically by ECB after activating ECB first time and describes what are the first basic steps:
M-x customize-option RET ecb-source-path RET1. This lets you customize the option
ecb-source-path with the customize-feature of Emacs. This opens
a customize-buffer where you can insert all the directories where ECB
can find your source-files. Save your changes with the button “Save
for future sessions” and then throw away this customize-buffer either
by killing it with
M-x kill-buffer or clicking at the button
M-x ecb-customize-most-important RETand see a list of options which you should at least know that these options exist.
The online-help of ECB is available via
(The section you are currently reading is part of the online-help of ECB)
The chapter “Common use-cases” is also very interesting!
 This means first hitting the keys M (Meta- or Alt-key) and x simultaneously, inserting “customize-option” in the minibuffer, hitting RETURN, inserting “ecb-source-path” in the minibuffer and finally hitting RETURN again