Learn Spanish (Latin America): La niña mira el pájaro atentamente.

Adverbs ending in -mente are the Spanish equivalent of English adverbs ending in "-ly". To make one, you take the feminine form of the adjective and add -mente. Here, the adjective for "attentive" is atento. We change it to the feminine form atenta and add -mente to get atentamente.

Does adding -mente change the written accent of the word?

When you add -mente to an adjective, the new word keeps the written accent mark if the original adjective had one. Since atento does not have a written accent, atentamente does not get one either.

Why doesn't mira have a preposition after it to mean "looks at"?

In Spanish, the verb mirar inherently means "to look at" or "to watch". You do not need to add a separate word for "at" because that meaning is already built into the verb.

Why is there no "personal a" before el pájaro?

The "personal a" is generally used before direct objects that are people, or sometimes specific pets you have a close emotional bond with. Since el pájaro is just a general animal here, it does not need the "personal a".