"Necesito hablar español."
Translation:I need to speak Spanish.
No, if you said "Necesito hablo español" you would be saying "I need I speak Spanish" which doesn't make sense in either language. Instead, you would say "hablar" which means to perform the action of speaking. "Necesito" is referring to who needs, and "hablar" refers to what exactly they need.
By using "hablo" you are changing the subject of the sentence from what you need to what you speak.
Elijah, the way it works is that the NECESITO translates as I NEED. And that is the main verb in the sentence. What follow is the secondary verb (in my terms) TO SPEAK, which is the infinitive, HABLAR. Hablar means, " to speak."
So you have, Necesito (I need ) hablar (to speak).
What's the difference between "I need to speak Spanish" and "I need to speak in Spanish"?
“I need to speak Spanish.” Is what we woukd say and it focuses on using the language. “I need to talk in Spanish” focuses on the conversation which just happens to be in Spanish. If you said “I need to speak in Spanish.” I might think that you are going to give a speech which happens to be in Spanish.
The verb form "necesito" is the conjugation for "yo" which means "I" and it is not used for anyone else. In Spanish the subject pronoun may be omitted, but in English the subject pronoun is always required except for the Imperative or command form for "you" which also doesn't look like this in Spanish.