From the within the Audit Log, click on the filter icon on the right hand side:

This will reveal the filter panel:

Using the filters available here you can search and view the activity as required. 

For example, should you wish to find out the activity of an individual between a certain timeframe select the options:

Please note: the Username field if the email address the user has been registered with.  This is to differentiate users with the same name.

This would then filter the audit log accordingly, and you can click on the item in the table to view more information.   For example, here we can see an event was updated with the consequence and likelihood scores being amended.

To clear any filters, click back on the filter icon, which will show red when filters are applied...

...and click, Clear Filters.