Nouns ending in -in are usually masculine.
(Words ending in -ain, -ein, -oin, -aim, or -uin follow different rules.)
Is magasin masculine or feminine?
lemagasin
The rule behind it
97.4% of -in nouns are masculine
In context
Je suis allé au magasin d'à côté.
I went to the store near by.
Le magasin vend des journaux et des magazines.
That store sells newspapers and magazines.
Allez tout droit et vous verrez le magasin.
Go straight on, and you will find the store.