Creating a contact group helps keep track of selected contacts. Example groups would be Buyer’s, Sellers, Companies, etc. The Groups feature allows you to email all group members simultaneously.

Click the Groups button located in the Contacts list

In the Group Details window, enter in a Group Name and a description.
Notice the Not In This Group and In This Group boxes.
Click on a contact to highlight, then click on the arrow to move them into the In This Group box. Repeat as necessary.

Be sure to click Save Group when finished.
(Reverse the process to remove a contact from a group)