How do I sort my contacts alphabetically by their last name?
By default, records are sorted by the time of record creation. In order to sort the contacts alphabetically by their last name, you have to change the name format order to Salutation, Last Name and First Name. Then you can click on the Contact Name column header in the list view and the records will be sorted by last name.
To change the name:
Click Setup > General > Personal Settings > Name Format.
Drag and drop the Last Name so that it comes next to the salutation and before the First Name.