Learn Spanish (Latin America): Yo como yogur en el desayuno.

Comer (to eat) is a regular verb ending in -er. To match the verb with yo (I), you drop the -er ending and add -o, which gives you como.

Do I have to include the word "Yo" at the beginning?

No, it is totally optional! Because the -o ending on como already tells us it means "I eat," the pronoun yo can be dropped. Native Spanish speakers usually leave it out unless they want to emphasize that they are the ones eating yogurt.

Why does it use "en" for "at breakfast"?

Prepositions rarely translate perfectly word-for-word between languages. While English speakers say "at breakfast" or "for breakfast," Spanish uses the phrase en el desayuno, which literally translates to "in the breakfast."

Why isn't it "como un yogur"?

When you are talking about consuming a general category of food or drink, Spanish often leaves out articles like un (a) or el (the). Just like in English, you are saying you eat "yogurt," not "a yogurt."