What's the right way to backups photos when using iPhoto? I have a folder called My-Photos where I have all my family photos.

Now I opened iPhoto app and import all those photos. Then I have the photo file in 2 places: My-Photos folder which I have created and in user/images/iPhoto Library which is the location where iPhoto storage all the information.

My question is. which folder should I backup to be sure that the originas photos are backup? 

If the answer is that I have to backup user/images/iPhoto Library then my question is which folder, because there are many folders in it... and some of them have a huge size.
Your iPhoto Library is contained within a database file on your computer. This file is located here:

/Users/(yourusername)/Pictures/iPhoto Library.photolibrary

That is the file (or technically, package file) that you will want to ensure is backed up to backup your iPhoto pictures.

As mentioned previously in comments, I recommend that you backup your entire hard drive instead of just your pictures. You can use a tool like Time Machine to backup to an external hard drive, or a service like CrashPlan to backup to the cloud.