Knowing when to use Soundtrack Pro vs when to bring a sound effect directly into Final Cut Pro is an aquired skill. In most cases if you are only bringing in one to three effects,. it is easier to just bring the sound effect right into Final Cut. An great way to accomplish this is to set your Spotlight to just search for music, preview the different options in Finder, and then drag the desired effect right into Final Cut. You can drag the effect directly form Finder into your Sequence, but if you may want to bring it into the File Browser first. Soundtrack Pro is great for assembling multi track audio, but if you only need one asset from Soundtrack Pro, you may want to consider this work flow.