Learn Spanish (Spain): Hoy hago la cena. - I am making dinner today.

Hago comes from the verb hacer (to do / to make). In Spanish, some verbs are completely regular except for the "I" (yo) form. Instead of following normal rules, hacer changes to hago for "I make". The other forms, like haces (you make), are regular!

The translation says "I am making", but isn't hago present tense ("I make")?

Yes! In Spanish, the simple present tense is often used for things happening right now or around now. Depending on the context, hago can mean "I make", "I do make", or "I am making".

Why do we say la cena ("the dinner") instead of just cena?

In English, we just say "dinner", but Spanish usually requires a definite article (el or la) before meals. So, "making dinner" is always hacer la cena.

Why isn't there a yo (I) at the beginning of the sentence?

Because the verb form hago can only ever mean "I make", the pronoun yo isn't necessary. Spanish speakers usually leave it out unless they want to emphasize that I am making dinner, as opposed to someone else.