When you install Mac OS X 10.4 Tiger and then restart your computer, the OS will automatically begin indexing your hard drive for Spotlight searching. Depending on how many files and Mail messages are on your hard drive, this can take anywhere from several minutes to a few hours. But once the process is done, searching for stuff on your computer using the Spotlight icon in the menu bar, or the Find command in the Finder, will take very little time.
While your hard drive is being indexed, your computer fans may run more than usual, your computer may seem "slow," and you may notice additional processor activity in Activity Monitor.
It's a good idea to allow your computer to finish its initial indexing before doing any processor-intensive work on it. Otherwise, the indexing may take longer. You can check its progress by clicking the Spotlight icon in the menu bar.
If you interrupt the process by restarting your computer or shutting it down, the indexing will resume at the next restart.