Learn Portuguese (Portugal): O senhor não é português.

In Portugal, o senhor (for men) and a senhora (for women) are used as a polite, formal way to say 'you'. You would use this when talking to someone older than you, a customer, or someone you do not know well.

If 'O senhor' means 'you', why do we use 'é' (he/she is) instead of 'és' (you are)?

Even though o senhor means 'you' in conversation, grammatically it acts like 'he' (ele). That is why it uses the third-person verb form é instead of the informal 'you' form és.

Where exactly does the word 'não' go when making a negative sentence?

In Portuguese, you simply put não directly before the verb to make it negative. Here, it goes right before the verb é, turning an affirmative statement into a negative one.

Why is 'português' written with a lowercase 'p'?

Unlike in English, adjectives for nationalities and languages are not capitalized in Portuguese unless they are at the very beginning of a sentence.