Learn Spanish (Latin America): Él es el amigo, pero no es de México. - He is the friend, but he is not from Mexico.

The accent mark changes the meaning of the word! Él (with the accent) means "he", while el (without the accent) is the masculine word for "the". Here, we have Él ("he") and el amigo ("the friend").

How would this sentence change if the friend were a woman?

You would change the masculine article el to the feminine article la, and the masculine noun amigo to the feminine noun amiga. The first half of the sentence would become Ella es la amiga ("She is the friend").

Why doesn't it say pero él no es de México in the second half?

In Spanish, you can drop the subject pronoun (like yo, tú, or él) if it is already clear who you are talking about. Since we established we are talking about him (Él) at the beginning, we can just say no es instead of repeating él es.

Why is the word no placed before es?

In Spanish, to make a sentence negative, you almost always put no directly before the verb. While in English we say "is not", the Spanish word order is closer to "not is" (no es).