pero

In a sentence

• Me gusta ese vestido, pero creo que es muy caro.

  I like that dress, but I think it's very expensive.

  Here, 'pero' is used as a conjunction introducing a contrast.

• Quería invitarte al cine, pero no sabía si estarías ocupado.

  I wanted to invite you to the movies, but I didn’t know if you would be busy.

  In this case, 'pero' is connecting two phrases, with the second providing an obstacle or reason for the inability to act on the first.

• El examen fue difícil, pero estudiando pude aprobarlo.

  The exam was difficult, but by studying I was able to pass it.

  Here, 'pero' presents a contrast between the difficulty of the exam and the positive outcome achieved through effort.