магазином

магазином

The Russian word "магазином" means "store" or "shop" (in the instrumental case).

Here 'магазина' refers to the genitive case of 'магазин' after the preposition 'мимо', indicating motion past the shop.

Я прошёл мимо магазина.

I walked past the shop.

Here 'магазином' is the instrumental case of 'магазин', used after the preposition 'за', indicating location behind the shop.

За магазином есть большая стоянка.

There is a large parking lot behind the shop.

In this case, 'магазином' is used in the instrumental case with the verb 'идти', meaning the action is taking place inside the shop.

Я иду магазином, осматривая полки.

I am walking through the shop, looking at the shelves.