Why do people who write in spanish always put a squiggly line over the e or n?

How do you say the following in spanish? 1. what are you going to do in school? 2. what will you do next year? 3. how hot is it going to get in town next month? 4. what college are you going to? 5. when will it get colder? 6. do you plan on getting married?

La administración no tenga ninguna idea para eliminar la corrupción. a. es necesario que b. es una vergüenza que c. es esencial que d. es importante que

Cuando julia va al campo escucha a las y a los caballos