Select Count(LastName), LastName
From YourTableName
Group By LastName
Having LastName Like "S*"
Order By LastName;
The group by is what count uses to match everything up. Whenever you use Group By, everything in your select clause must also be in the Group By.
The Having clause is like a Where clause for Group By. In the example above, it would return all LastNames starting with S.
Good Luck!