Learn Hardcore Spanish (Spain): Quiero ayudar al profesor.

In Spanish, when the preposition a (meaning “to”) is followed by the masculine article el, they contract into al. So a + el becomes al. That’s why you never see a el profesor, but always al profesor.

Do I need to include the subject pronoun yo at the beginning of the sentence?

It’s not necessary in Spanish because the verb ending (-o in quiero) already indicates the subject is the speaker (I). You can say Yo quiero ayudar al profesor, but most Spanish speakers just say Quiero ayudar al profesor.

Why is it quiero instead of quieres or quiere?

Quiero is the first-person singular (I) form of querer (to want).
• Quiero: I want
• Quieres: you (informal) want
• Quiere: he/she/you (formal) want(s)

How would this sentence change if the teacher is female?

You would change profesor (masculine) to profesora (feminine) and keep the contraction if applicable.
So it becomes Quiero ayudar a la profesora. Notice that with “la” instead of “el,” there is no contraction.