Hi Olaedo,

There are eight verbs that can take either avoir or être. Passer is one of the eight.

These verbs are able to be used with or without an object and this aspect is known as transitivity.

Non-transitive or transitive usage. Transitive usage - avoir. Non-transitive usage - être.

In the case that you are querying "Ma tante est passée (state of being) par la boulangerie en venant ici"

This means that your aunt took a brief visit to the bakery whilst en route. 

"Nous avons passé une semaine à Madrid l'été dernier." In this case "Une semaine" the direct object of the verb passer.

Hope this helps.

Jim