Learn Hardcore Russian: С северной стороны дворца растут старые деревья, а с южной — цветы. - On the northern side of the palace old trees grow, and on the southern side there are flowers.

Breakdown of С северной стороны дворца растут старые деревья, а с южной — цветы.

What does the preposition с mean in с северной стороны дворца? Is it “with”, “from”, or “on”?

In this sentence, с means “from / on the side (facing something)”, not “with”.

Literally, с северной стороны дворца = “from the northern side of the palace”.
In practice, it’s often understood as “on the northern side (of the palace)”—it describes which side of the building something is on / comes from.

This is a very common pattern in Russian:

Why is it с северной стороны, not с северная сторона? What case is that?

Северной стороны is in the Genitive singular (feminine):

The preposition с in the sense “from (a surface, edge, side)” always takes the Genitive:

So you must say с северной стороны, not с северная сторона.