Learn Spanish (Latin America): Yo no veía el kiosco aquí.

It is slightly irregular because it keeps the e from the infinitive ver. A truly regular verb drops the entire -er ending before adding -ía (for example, comer becomes comía). If ver were completely regular, it would become vía, which is not a real word! Instead, we get veía.

Why does the translation say "used to see" instead of just "didn't see"?

The imperfect tense describes ongoing, background, or repeated actions in the past. Translating it as "did not use to see" perfectly captures that this was an ongoing, habitual situation over a period of time, rather than a single event. If it were a single, one-time event, you would use the preterite tense (vi).

Do I have to include yo in this sentence?

You do not have to, but it is very common and helpful in the imperfect tense. The yo (I) form and the él/ella/usted (he/she/you formal) forms are identical in this tense: they are both veía. Including yo prevents confusion and makes it perfectly clear who you are talking about.

What exactly is a kiosco in Latin America?