You can use your microphone to do a lot of things. Sure, web cam and video chat. If you want to use it to do your search then go to Google's home search page. In the search bar where you type is a picture of a microphone, click it and record, that's it.
Voice search didn't pick up my voice. Then I saw in the lower left of gmail "call phone". I made a call and it worked fine. Then I went back to Google search and tried it again and now it works. Lesson learned: Just keep digging.