cu

In a sentence

• Am plecat cu trenul la București.

  I left with the train to Bucharest.

  In this sentence, 'cu' expresses the means of transportation, indicating the tool or method by which the action of leaving was performed.

• Merg la cinema cu prietenii mei.

  I am going to the cinema with my friends.

  Here, 'cu' denotes companionship, showing that the action of going is done in the company of others.

• Scriu cu un stilou nou.

  I am writing with a new pen.

  In this example, 'cu' indicates the tool or instrument used to perform the action of writing.