Hey Alejandro -
Your Portfolio is what people will see when they view your profile and this is the most important part of being on Behance. Yours is found here: http://www.behance.net/AlejandroLorenzo
Collections are just a way that you can be making sets of work that you admire or want to save in some way. These are just ways to explore Behance, don't think of them as "collections of your work," that's what your Portfolio is. Collections are a way to save work you like from others. But, if you did want to add your own work to a collection, you'd just view your own project and click "add to collection" in the right hand side column.
Hope this helps clarify!
Thanks, yes. Now I see it