This is the 8518th most frequent Polish word.
poznań
Poznań: A city in western Poland.
In this sentence, 'Poznań' is used as a proper noun referring to the name of the city.
Poznań to piękne miasto w Polsce.
Poznań is a beautiful city in Poland.
Here, 'Poznań' again refers to the city as a geographical location visited during travel.
Odwiedziłem Poznań w zeszłym roku.
I visited Poznań last year.
In this sentence, 'Poznania' is the genitive case of 'Poznań', reflecting possession or relation, and refers to the city.