The preferences menu will also let you set other elements of the plugin, like whether you want find as you type or not. You can also configure your default search channel, if you want a channel image or not, if search results should open in a tab and many more.
AcidSearch itself is really easy to use. Clicking on the little arrow in your search bar will reveal your menu of different search channels. Just select the one you wish to use to make it active.
AciSearch is the ideal companion to the Safari search bar, which I personally feel is a bit limited.
Set find as you type
Set search bar actions
Add and organize channels
Search bar can feel overloaded
AcidSearch also allows you to access your search channels with key equivalents, shortcuts (a la SafariKeywords), and a contextual menu. It patches Safari using Mike Solomon's great SIMBL InputManager. AcidSearch is free software, and will always be free. If you like AcidSearch a lot, and wish to reward me for my development efforts, you are welcome to donate. AcidSearch is available in English, Japanese, Italian, French, and traditional Chinese.