Hi @jibberjab,

All of them are part of the same functionality:

Twitter plugin "Ping" = automatically publish a tweet to your twitter account taking parts of your post to compose it.

1. System - Plugins - Twitter Plugin: common settings of the plugin. Let you install/unistall, enable/disable, etc, as any other plugin.
2. Collections - BlogName - Plugins - Twitter Plugin: per-collection twitter plugin settings. You can link each collection to a different twitter account. There is also the possibility to set different messages to each collection.
3. Collections - BlogName - Settings - Advanced - After each new post...: all the Ping plugins (as Twitter) available for the current collection are centralized in the same list, so you can decide which of them enable/disable whenever you want with a single click. Let's say you don't want to send to twitter your next post, so you uncheck it here and publish your post as usual, that way there is no need to make any other change.

Regards!

@jibberjab you will also find updated info here: http://plugins.b2evolution.net/twitter_plugin

Note: @mgsolipa This is a classic case that should trigger a clean-up / rewrite of a few man pages.