An exercise is an interactive element that a student uses to try out a concept or tool. The more students are forced to use what they are learning, the better students retain the information. An exercise comes in a couple of different formats.
There might be a resource on the Internet or your company's Intranet that you want the student to try. You can provide a link to the resource along with an exercise the student can perform when they are accessing the resource.
You can use a simple interactive yes/no or multiple-choice questionnaire to help students understand the effect of different choices.
You may want to create a simulation of a tool or technology about which students are learning.