Chico is a masculine noun meaning boy. That is why it uses the masculine singular article el.
The article and the noun have to match in gender and number.
Spanish often uses the present tense for narration, especially in examples, dialogues, captions, or storytelling. So El chico responde is a very natural way to introduce what the boy says.
Depending on context, Spanish could also use a past tense, for example:
But in a simple dialogue line or example sentence, the present is very common.
That is just how the fixed expression works in Spanish. Word-for-word, de nada looks like of nothing, but you should learn it as a whole phrase meaning you’re welcome.
Many everyday expressions do not translate literally between languages, so it is better to treat De nada as one complete unit.
« » are called angle quotes or guillemets. They are traditional quotation marks in Spanish typography.
So in Spanish, it is very normal to see:
You may also see:
especially in modern publishing, online writing, or depending on style guides. Both can appear, but « » are especially associated with standard Spanish punctuation.
A simple pronunciation guide is:
More roughly in IPA for Spain: /resˈponde/
A few points:
Yes, Spanish often drops subject pronouns, and sometimes even the full subject if it is already clear from context.
So both are possible:
The version with el chico is clearer because it explicitly tells you who is speaking. It is useful when introducing a scene, a story, or an example sentence.
Often, yes. Both can mean to answer / to reply.
Both are possible in many contexts.
Very generally:
In this sentence, responde sounds completely natural.