how do I know 2 viruses were really blocked in past 30 days?

[REDACTED]

Under the component status section, it states that 2 VIRUSES WERE BLOCKED IN THE PAST 30 DAYS.   

It doesn't let me click anything to see what was blocked.  Where are the logs?  How do I know Avast is blocking anything?   

[DavidR]

First can you not recall an avast alert on your system ?

AvastUI > Scan > Scan for viruses - at the bottom of that window - Scan History.

This will give a list of scans you have done, you have to select a scan that has had a detection and then Detailed report.

This however is for on-demand scans and won't include detections by the web shield, etc.

[Eddy]

How do I know Avast is blocking anything?

You already answered it yourself. "Under the component status section, it states that 2 VIRUSES WERE BLOCKED IN THE PAST 30 DAYS."

The location of the log files depend on what OS you are using.
All possible locations are mentioned on the avast website as well as in many threads on this webboard.

What is recorded in the logs depends on your settings.