I want to create a structure in Joomla for users. A different article for different registered users. I do not have groups. For example If I have 3 users, and when they click on a menu (for example, "Info") they see a different article from each other.
User A sees something different when he clicks on info and user B something else and user C something else.
How can I do this; are there any components?
There is no feature in Joomla or extensions that I know of that allows you do this. If you are using Joomla 2.5/3.0, then you will be best off creating different user groups, then creating 3 separate menu items, 1 for each group that only they have access to.
If you are Joomla 1.5, then you only extension that I know of for adding custom user groups is ArtofUser, which is still limited in it's own way.