There are many different types of logs and reports available in Moodle. Teacher and administrator report logs are very similar. Teachers can not see information outside of a course.
A log can be thought of as a list of information, some might call it a table. Each line or record in the log usually contains a timestamp plus one or more fields that holds information about activity at that instant. A report presents the content of the log in some sort of uniform format. Different reports can use the same log. For example different reports might have different sort orders and sub groupings. Filters selectively reduce or focus the information shown in the report. In Moodle, a log report is a process where the administrator or teacher can customize a one time report about activity.
In short, there are other MoodleDoc pages that deal with very specific reports.
Teacher log reports
show activity within the course. It allows tutors to see what resources are being used and when. For example a teacher can check that an individual student has viewed the resource they claim to have read, and how long. Individual user reports generate some basic graphical views of this information.
The drop-down menus are used to set filters. The teacher can view the log records at course level, user level and/or activity level on a specific day or all days. When groups are enabled in a course, that will be another option.
For course management these logs can help determine what types of resource are the most popular, including those that receive no interest whatsoever. This can help plan resource selection for future courses. Viewing individual activity reports can help you monitor student activity and identify learning styles.
Administrator log reports
These are available to someone with site administrative rights and are found in the Site administration block. There are filters for user, course, and activity types. There is predefined log report which shows all activity in the last hour on the site. Moodle1.7