Hi @Allan Rocha,
 

1. Add a calendar to your site.
2. Open the Nintex Workflow designer from the ribbon.
3. Click the import button and import the workflow.

Repeat steps 2 and 3 for each workflow you want to add to the calendar.

To add to Simon’s answer, if you go to the Calendar settings on your original calendar, you can save the template of it. This template will be saved to the site itself, and contains all settings specific to that calendar: columns, Nintex form (including rules), validation on columns, created views, settings, and so on, it just doesn’t save the calendar permissions. Then you can go to the Site settings and find the template under the List template settings and download it from there. You can then upload the same template to the site you want to bring the calendar over to in the same place under the Site settings. Once it’s there you can add the calendar to the new site through “add a new app”, and it will create it with all the settings and the Nintex form already available from the template. It helps a lot when you then import the list workflows, they will also immediately recognize the columns on their own calendar they have to reference through actions or workflow settings.

Thank you guys!

I already put the workflow in my calendar, but now I have another problem. 

I just have the skeleton of the workflow but now I have to configurate all the steps. You know some guide that I can use to understand how it works every step of the workflow? I'm very lost, first time using Nintex.

And again, thank you so much for the support! 

Without knowing what your workflow has to do or what your goals are I can’t give any specific advice, and giving a full on tutorial here is a bit much for a single post, but you could check out this overview that details most actions and gives (very short) explanations.