Updated for 7.0
On the left-hand side of the screen in the navigation bar, select Group(s) under Member. This will take you here:
Click on the group to which the lieutenant belongs. This will take you here:
In the Sr. Lieutenant box on the right, click the box with an envelope icon.
A box in which you can write your message will pop up that will look like this:
Here, follow the prompt to fill in the subject title
Below that, type your message where it says Message.
When finished, click the Send Message button.
These are samples.