Moodle provides several built-in reporting options that show student access data to your Moodle site.
Course participation allows you to break down student engagement by a particular activity you've added to your course.
If you'd like to examine student engagement on a granular level, you can have a look at the Logs, and if you want overall activity, try Activity report for a general sense of all that's been happening in your course.
For more information, please check out Use Reports to Track Student Activity in Moodle (UMass).