If You want scan a single file use clamscan Path/to/File
If You want scan something in a Directory clamscan -r Path/to/Directory
And if You want simply scan Your wohle System clamscan -r /
Of Course, You have a lot of Options that You can activate or deactivate. You get an Overview when You type clamscan --help
I personally use ClamTk because I find it with the graphical Interface easier.