Save sqlwhereoperators.php as sqlwheremultiple.php. Replace the current query with this to show all females with the family name Perry:
SELECT ref, dob, personal, family, gender, doj FROM employees WHERE gender='F' AND family='Perry';
That should give you just three results. Now change the ='Perry' to !='Perry'. That should give you all the females apart from those called Perry.
Change the AND to OR. Now you have all the females but also all males as long as there name is not Perry. You can combine these techniques to make very complicated queries. Try this one in place of yours:
SELECT ref, dob, personal, family, gender, doj FROM employees WHERE gender='F'AND (family='Perry' OR family='Ritzman' OR family='Esposito');
The brackets make it clear that you want all people who are female AND have any of those three names. Remove the brackets and you will see a male in the list which now includes females called Perry and anyone (OR) called the other two names.
You can use combinations of brackets with AND and OR to select many different things. Try this:
SELECT ref, dob, personal, family, gender, doj FROM employees WHERE (gender='F'AND family='Perry') OR (gender='M' AND family='Esposito');
That should give you the three females with the family name Perry and one male with the family name Esposito.
Try to understand those principles but don't worry about the details. Combine AND and OR with the operators you just learned about and you should be able to select almost anything from a database.