by

In a sentence

• Aquest llibre ha estat escrit per un autor famós.

  This book was written by a famous author.

  This usage denotes identification of the agent responsible for the action of writing the book.

• Vaig arribar a casa per la carretera principal.

  I arrived home by the main road.

  Here, 'by' indicates the manner or path used to accomplish the action, specifying the route taken.

• Vaig passar per la biblioteca abans de tornar a casa.

  I passed by the library before returning home.

  In this context, 'by' shows proximity or the act of moving past a location during the action.