Learn Russian: Это северный город.

In Russian, the verb "to be" (is, am, are) is almost always skipped in the present tense. Instead of saying "This is a northern city", you just say "This a northern city".

город (city) is a masculine noun. Why do we use the neuter word это instead of the masculine этот?

When you are introducing or pointing something out by saying "This is...", you always use the fixed word это, no matter the gender of the noun. You only use the masculine этот if you are saying "this city" (этот город) to describe a specific item, like in the sentence "This city is cold."

What part of the word северный (northern) shows that it matches the masculine noun город?

The ending -ый is a very common ending for masculine adjectives. Adjectives must match the gender of the noun they describe. If it were describing a feminine noun, it would end in -ая, and for a neuter noun, it would end in -ое.

How are the two "o" vowels pronounced in город?

The stress is on the first syllable, so the first "o" makes a normal, clear "o" sound. In Russian, an unstressed "o" is reduced and sounds like an "a". This means the second "o" sounds much more like the "a" in "about" or "uh".