Using the Import button in ILA toolbar you can open the Import window which has 3 tabs Settings, Calendar and Manually import.
In the Calendar tab you can see a whole year calendar in which some days have small colored corner with different colors.

Colored corners means that there exist log files in the base log directory for the displayed day.
Colors are different for different log file types:
After log files are imported the colors changes and occupy the entire area for that day (or square) as in the following image:

Right clicking on a day you get a pop-up menu that lets you import log files of that day. Its useful, since most administrators prefer to configure ILA importing logs of the previous day, during late night, due to performance reasons. Thus, if you want to do an analysis of something that happened after the last import, such as an email sent or received through SMTP, right button click and choose to import the SMTP log for that day, as shown below.

Single SMTP Logs
To import a single SMTP log, double-click the Database connections <internal> Import left pane tree item. The usual Open dialog allows you to browse for a single SMTP log file.
Import of Current Day Logs
To import logs for a current day, you can create a batch file with the -dtoday switch.