Learn Portuguese (Portugal): Vocês caminharam comigo anteontem. - You pl. walked with me the day before yesterday.

We are using the simple past tense for vocês (you plural). For regular verbs ending in -ar like caminhar (to walk), we drop the -ar and add the ending -aram. Notice that vocês shares the exact same verb ending as eles and elas (they).

How do I pronounce the -am at the end of caminharam?

The -am ending does not sound like a hard English M. Instead, it creates a nasal OW sound. Also, be careful with where you put the emphasis: in the past tense ending -aram, the stress falls on the syllable just before the R, so the strongest part of the word is -nha-.

Why do we use comigo instead of combining com (with) and mim (me)?

In Portuguese, you cannot say com mim or com eu to mean with me. They always merge into the special single word comigo.

Is anteontem made up of two words?

Yes! It is a combination of the prefix ante- (before) and the word ontem (yesterday). Put them together, and you get before yesterday, which is exactly how Portuguese says the day before yesterday.