Running ClamXav
Step 1:
Click the ClamXav icon on your dock at the bottom of the screen.
Step 2:
Click the Choose what to scan button.

Step 3:
Click Macintosh HD on the left window.

Step 4:
Click the top entry in the center window (eg. Applications). While holding the Shift key on your keyboard, click on the bottom entry (eg. Users).
When you do so, this should highlight all folders in the center window.
Then, click the Open button.

Step 5:
Click the Start Scan button. Please be patient, as the scan may take some time.

Step 6:
When the scan is complete, a scan summary will be displayed in the bottom window, including a list of files that were disinfected.
Congratulations! You have successfully scanned your computer with ClamXav.