Act I scene 3 is where you need to look to find the answer you are looking for. This is when Lady Capulet and the Nurse tell Juliet some potentially exciting news about her future as they try to get her to think about marriage. Note what Lady Capulet says to her:
Then think of marriage now...
The valiant Paris seeks you for his love.
We need to remember that in Juliet's context, marriage was not something that a lady of Juliet's social status that was decided based on love or mutual feeling. For Juliet, the daughter of a great and noble household of Verona, marriage was always going to be something that would be ultimately decided by her parents and would be decided with the goal of forging new alliances or gaining wealth and territory. Marriage would be something that she would have little say over. Therefore, this scene clearly indicates the way in which Juliet's freedom is being compromised by the news that Paris seeks her hand and wishes to marry her.