1. A method for exploring a catalog of digital information contents through a user apparatus comprising a display screen, in which said catalog of digital information contents is structured according to at least two hierarchical tree structures each comprising a respective hierarchy of nodes, each node corresponding to a respective category of digital information contents, comprising: selecting a first sub-hierarchy of nodes of a first one of said at least two hierarchical tree structures, said first sub-hierarchy of nodes being built beginning from a selected category of said first hierarchical structure by selecting at least one among a first number of categories at immediately higher hierarchical levels with respect to the selected category and a second number of categories at immediately lower hierarchical levels with respect to the selected category; selecting a second sub-hierarchy of nodes of a second one of said at least two hierarchical tree structures, said second sub-hierarchy of nodes being built beginning from a destination category of said second hierarchical structure, said destination category being in relationship with said selected category, by selecting at least one among a first number of categories at immediately higher hierarchical levels with respect to the destination category and a second number of categories at immediately lower hierarchical levels with respect to the destination category; simultaneously displaying on the screen, icons representative of all of the categories of the selected first and the selected second sub-hierarchy and respective relationships between the categories, wherein each of the icons represents only one category, and an icon of the icons representing the selected category at least partially overlaps an icon of the icons representing the destination category; and exploring the categories of the first and of the second sub-hierarchy by reacting to commands imparted by a user through said user apparatus.